splitting voltage

[randomname]

hello everyone.

ive been working on a project for awhile, and im so close to completion
exception for one little problem. im trying to power a small DC motor,
as well as about 20 3mm LEDs, but am running into timing issues when
the pump is powered.

the circuit is:

a 555 timer, whose frequency is around 30Hz; most of the time the
output is +, when it is - its only for an extremely short amount of
time (its a strobe light, basically). the output of this timer goes to
20 parallel 3mm LEDs to positive (no resistor, since theyre not on for
long enough to burn). just to be clear, to output of the 555 is:

++++++++++-++++++++++- (at about 30Hz). when it's -, the LEDs go on.

this works fine, until the second part of the project is introduced.
id like to run a small battery powered water pump (it takes two 2x C
batteries) but I'd like it to run on the power supply of the
aformentioned circuit (4x AA batteries). im not quite sure how to do
this. the "pump" is just a small DC motor about an inch in diameter.
i do not know the amperage rating of it.

i wont even go over what i tried at the risk of sounding like a fool.
whats the best way to run both the motor and the 555 timer + LEDs?

thanks a ton,
-sam

 

[James Thompson]

hello everyone.

ive been working on a project for awhile, and im so close to completion
exception for one little problem. im trying to power a small DC motor,
as well as about 20 3mm LEDs, but am running into timing issues when
the pump is powered.

the circuit is:

a 555 timer, whose frequency is around 30Hz; most of the time the
output is +, when it is - its only for an extremely short amount of
time (its a strobe light, basically). the output of this timer goes to
20 parallel 3mm LEDs to positive (no resistor, since theyre not on for
long enough to burn). just to be clear, to output of the 555 is:

++++++++++-++++++++++- (at about 30Hz). when it's -, the LEDs go on.

this works fine, until the second part of the project is introduced.
id like to run a small battery powered water pump (it takes two 2x C
batteries) but I'd like it to run on the power supply of the
aformentioned circuit (4x AA batteries). im not quite sure how to do
this. the "pump" is just a small DC motor about an inch in diameter.
i do not know the amperage rating of it.

i wont even go over what i tried at the risk of sounding like a fool.
whats the best way to run both the motor and the 555 timer + LEDs?

thanks a ton,
-sam

Just solder a tap at the halfway part of the battery holder to run the
motor. Also why not switch the battery hold to use all C cells unless space
is an issue.

 

[randomname]

Just solder a tap at the halfway part of the battery holder to run the
motor. Also why not switch the battery hold to use all C cells unless space
is an issue.

thats a good idea, however the battery holder is a weird rectangular
prism shape. plus, id like to learn about how to do this.

- -
| |
resistor 555
| | [pin 3]
motor LEDs
| |
+ +

when I connect the motor, the LEDs will flicker much faster and dont
hold a steady brightness. why would this cause the 555 timer to
oscillate faster and sporadically? im confused.

-sam

 

[James Thompson]

Just solder a tap at the halfway part of the battery holder to run the
motor. Also why not switch the battery hold to use all C cells unless
space
is an issue.

thats a good idea, however the battery holder is a weird rectangular
prism shape. plus, id like to learn about how to do this.

- -
| |
resistor 555
| | [pin 3]
motor LEDs
| |
+ +

when I connect the motor, the LEDs will flicker much faster and dont
hold a steady brightness. why would this cause the 555 timer to
oscillate faster and sporadically? im confused.

-sam

You may want to try using a 100 uH inductor in series with the motor and
even a 1n4002 diode reverse biased in parallel to the motor, as the motor
may be producing current pulses on the supply voltage. The inductor should
help block it. Also try adding an electrolytic cap of about 220 uF to the
battery feed to smooth out the varying current the motor is causing. Does
the voltage hold steady when the motor runs, or is there a big drop? A 555
timer functions via a voltage divider internally, so if the voltage source
varies - so does its timing.

 

[vic]

Just solder a tap at the halfway part of the battery holder to run the
motor. Also why not switch the battery hold to use all C cells unless space
is an issue.

you need to avoid this. The batteries powering the motor will discharge
faster than the other batteries and the fresher batteries will continue
to push current through them even after they're dead, which can lead to
leaks and other nasty behaviour.

vic

 

[randomname]

You may want to try using a 100 uH inductor in series with the motor and
even a 1n4002 diode reverse biased in parallel to the motor, as the motor
may be producing current pulses on the supply voltage. The inductor should
help block it. Also try adding an electrolytic cap of about 220 uF to the
battery feed to smooth out the varying current the motor is causing. Does
the voltage hold steady when the motor runs, or is there a big drop? A 555
timer functions via a voltage divider internally, so if the voltage source
varies - so does its timing.

Which should I try first, the inductor or the diode? I think you are
right about the motor producing pulses, because if I just do:

-
|
555 timer
|
LEDs
|
+

along with

-
|
10ohm (10w)
|
+

the 555 timer works normally, whereas when I connect the motor it
freaks out.

I'm not sure I understand what you want me to do with a 220uf
capacitor.

Thanks for your help,
-sam

 

[default]

- -
| |
resistor 555
| | [pin 3]
motor LEDs
| |
+ +

It is going to take more information. Regarding the motor - just a
resistor and motor will work if you know how much current the motor
requires it is easy to calculate the value of the resistor. Half the
voltage will be wasted as heat in the resistor.

An alternative to wasting the power (and it is likely the capacity of
4 AA cells won't come close to the run time you get with two C cells)
is to chop the power to the motor. You build another 555 astable
multivibrator with a 50% duty cycle. It runs too fast for the motor
so you won't notice the speed changing, yet you only use half the
power. Similar to what you are doing to keep the LEDs from burning
out. Another advantage - if you make it variable duty cycle you can
control the pump and maybe use less battery power.

Search for: Pulse Width Modulated (or pwm) DC motor speed controller,
lot of circuits on the net

when I connect the motor, the LEDs will flicker much faster and dont
hold a steady brightness. why would this cause the 555 timer to
oscillate faster and sporadically? im confused.

-sam

You don't show your schematic but I'd expect to see that with a
battery supply and a motor load against a 555

The battery voltage changes with the motor load. If the voltage to
the 555 power supply changes it is likely to trigger later or earlier
in its normal timing cycle - you need to supply the led timer with a
seady source of power.

One cheap and easy way to do it would be to add a rectifier diode to
the 555 power input pin (pin 8 and 4 on the astable). Its purpose is
to only allow current to flow into the 555 not back to the motor. You
put a relatively large capacitor on the supply and ground on the 555
side of the diode. A few thousands of microfarads at 6 volts.

Something you should already have is a bypass capacitor on pin 5 to
ground (that helps keep the voltage steady on the internal divider
string on the 555 and keeps the trigger voltage from wandering around.
I think the application notes call for .01 microfarad, but with a slow
oscillator and big problems I'd try more - up to a microfarad.(and
this may have a deleterious effect on the start up flashing of the
LEDs so the timing may be off until the cap charges). 01/.1 won't be
noticed and may help some.

The problem is you motor is sucking too much power from the batteries
and represents a varying load (with a brush type motor especailly).
The 555 really wants a clean steady source of power, so either the
power supply has to be stiffer (large caps, large batteries) or the
motor load has to be lower, or both.

The inductance in the motor and brushes create electrical noise as
each commutator segment swings by the brush. It wouldl be a very good
idea to put a ceramic disk capacitor as close to the motor brushes as
possible (right at the housing to the motor and across its power
leads) .1uf 50 volts ought to be goood. Noise can trigger a 555.

Other tricks - good physical layout. Run a seperate wire from the 555
power and ground all the way back to the battery pack. Do the same
thing with the motor - the wire should not carry the current for both
the motor and 555, that's asking for trouble.

 

[randomname]

- -
| |
resistor 555
| | [pin 3]
motor LEDs
| |
+ +

It is going to take more information. Regarding the motor - just a
resistor and motor will work if you know how much current the motor
requires it is easy to calculate the value of the resistor. Half the
voltage will be wasted as heat in the resistor.

An alternative to wasting the power (and it is likely the capacity of
4 AA cells won't come close to the run time you get with two C cells)
is to chop the power to the motor. You build another 555 astable
multivibrator with a 50% duty cycle. It runs too fast for the motor
so you won't notice the speed changing, yet you only use half the
power. Similar to what you are doing to keep the LEDs from burning
out. Another advantage - if you make it variable duty cycle you can
control the pump and maybe use less battery power.

Search for: Pulse Width Modulated (or pwm) DC motor speed controller,
lot of circuits on the net

when I connect the motor, the LEDs will flicker much faster and dont
hold a steady brightness. why would this cause the 555 timer to
oscillate faster and sporadically? im confused.

-sam

You don't show your schematic but I'd expect to see that with a
battery supply and a motor load against a 555

The battery voltage changes with the motor load. If the voltage to
the 555 power supply changes it is likely to trigger later or earlier
in its normal timing cycle - you need to supply the led timer with a
seady source of power.

One cheap and easy way to do it would be to add a rectifier diode to
the 555 power input pin (pin 8 and 4 on the astable). Its purpose is
to only allow current to flow into the 555 not back to the motor. You
put a relatively large capacitor on the supply and ground on the 555
side of the diode. A few thousands of microfarads at 6 volts.

Something you should already have is a bypass capacitor on pin 5 to
ground (that helps keep the voltage steady on the internal divider
string on the 555 and keeps the trigger voltage from wandering around.
I think the application notes call for .01 microfarad, but with a slow
oscillator and big problems I'd try more - up to a microfarad.(and
this may have a deleterious effect on the start up flashing of the
LEDs so the timing may be off until the cap charges). 01/.1 won't be
noticed and may help some.

The problem is you motor is sucking too much power from the batteries
and represents a varying load (with a brush type motor especailly).
The 555 really wants a clean steady source of power, so either the
power supply has to be stiffer (large caps, large batteries) or the
motor load has to be lower, or both.

The inductance in the motor and brushes create electrical noise as
each commutator segment swings by the brush. It wouldl be a very good
idea to put a ceramic disk capacitor as close to the motor brushes as
possible (right at the housing to the motor and across its power
leads) .1uf 50 volts ought to be goood. Noise can trigger a 555.

Other tricks - good physical layout. Run a seperate wire from the 555
power and ground all the way back to the battery pack. Do the same
thing with the motor - the wire should not carry the current for both
the motor and 555, that's asking for trouble.

Thank you so much for this info.

I've drawn up a schematic...

http://img217.imageshack.us/my.php?image=circuitcs2.jpg

I've changed the supply to 2x C batteries, and added a diode in
parallel to the motor.

Do you think this would work?

 

[ehsjr]

- -
| |
resistor 555
| | [pin 3]
motor LEDs
| |
+ +

It is going to take more information. Regarding the motor - just a
resistor and motor will work if you know how much current the motor
requires it is easy to calculate the value of the resistor. Half the
voltage will be wasted as heat in the resistor.

An alternative to wasting the power (and it is likely the capacity of
4 AA cells won't come close to the run time you get with two C cells)
is to chop the power to the motor. You build another 555 astable
multivibrator with a 50% duty cycle. It runs too fast for the motor
so you won't notice the speed changing, yet you only use half the
power. Similar to what you are doing to keep the LEDs from burning
out. Another advantage - if you make it variable duty cycle you can
control the pump and maybe use less battery power.

Search for: Pulse Width Modulated (or pwm) DC motor speed controller,
lot of circuits on the net

when I connect the motor, the LEDs will flicker much faster and dont
hold a steady brightness. why would this cause the 555 timer to
oscillate faster and sporadically? im confused.

-sam

You don't show your schematic but I'd expect to see that with a
battery supply and a motor load against a 555

The battery voltage changes with the motor load. If the voltage to
the 555 power supply changes it is likely to trigger later or earlier
in its normal timing cycle - you need to supply the led timer with a
seady source of power.

One cheap and easy way to do it would be to add a rectifier diode to
the 555 power input pin (pin 8 and 4 on the astable). Its purpose is
to only allow current to flow into the 555 not back to the motor. You
put a relatively large capacitor on the supply and ground on the 555
side of the diode. A few thousands of microfarads at 6 volts.

Something you should already have is a bypass capacitor on pin 5 to
ground (that helps keep the voltage steady on the internal divider
string on the 555 and keeps the trigger voltage from wandering around.
I think the application notes call for .01 microfarad, but with a slow
oscillator and big problems I'd try more - up to a microfarad.(and
this may have a deleterious effect on the start up flashing of the
LEDs so the timing may be off until the cap charges). 01/.1 won't be
noticed and may help some.

The problem is you motor is sucking too much power from the batteries
and represents a varying load (with a brush type motor especailly).
The 555 really wants a clean steady source of power, so either the
power supply has to be stiffer (large caps, large batteries) or the
motor load has to be lower, or both.

The inductance in the motor and brushes create electrical noise as
each commutator segment swings by the brush. It wouldl be a very good
idea to put a ceramic disk capacitor as close to the motor brushes as
possible (right at the housing to the motor and across its power
leads) .1uf 50 volts ought to be goood. Noise can trigger a 555.

Other tricks - good physical layout. Run a seperate wire from the 555
power and ground all the way back to the battery pack. Do the same
thing with the motor - the wire should not carry the current for both
the motor and 555, that's asking for trouble.

Thank you so much for this info.

I've drawn up a schematic...

http://img217.imageshack.us/my.php?image=circuitcs2.jpg

I've changed the supply to 2x C batteries, and added a diode in
parallel to the motor.

Do you think this would work?

Better would be this:

+6 ----+------+----[Inductor]---+-----+
| | | |
[C1] [555 & Leds] [C2] [555 PWM]--motor
| | | |
Gnd----+------+-----------------+-----+

In other words, keep the 4 cell supply and the existing
555/transistor/LED circuit. Add the recommended capacitor
at C1. (It connects from pin 8 of the 555 to pin 4 of the
555.) Build the 555 PWM/transistor circuit. Add the recommended
inductor. Add another cap as shown at C2 (again, connects from
pin 8 to pin 4). Don't forget the diode in parallel with
the motor, with the banded end to the + side.

On the each 555, be sure to add a .01 uF cap from pin
5 to ground.

Ed

 

[randomname]

Thank you so much for this info.

I've drawn up a schematic...

http://img217.imageshack.us/my.php?image=circuitcs2.jpg

I've changed the supply to 2x C batteries, and added a diode in
parallel to the motor.

Do you think this would work?

Better would be this:

+6 ----+------+----[Inductor]---+-----+
| | | |
[C1] [555 & Leds] [C2] [555 PWM]--motor
| | | |
Gnd----+------+-----------------+-----+

In other words, keep the 4 cell supply and the existing
555/transistor/LED circuit. Add the recommended capacitor
at C1. (It connects from pin 8 of the 555 to pin 4 of the
555.) Build the 555 PWM/transistor circuit. Add the recommended
inductor. Add another cap as shown at C2 (again, connects from
pin 8 to pin 4). Don't forget the diode in parallel with
the motor, with the banded end to the + side.

On the each 555, be sure to add a .01 uF cap from pin
5 to ground.

Ed-

I don't quite follow.. what are the recommended capacitors C1 and C2?

Also, where does the inductor connect? (from positive to positive?)

Thanks,
-sam

 

[default]

I've drawn up a schematic...

http://img217.imageshack.us/my.php?image=circuitcs2.jpg

I've changed the supply to 2x C batteries, and added a diode in
parallel to the motor.

Do you think this would work?

No

The standard 555 timer requires a minimum of 4.5 volts to work. 3
volts probably won't cut it. One of the Cmos versions might work but
some of the parts values would have to change

And if you're shooting for a 50% duty cycle it seems logical to me
that the resistor values you show are not going to work - and if you
are using 3 volts you don't need the 50% duty cycle anymore (the whole
purpose was to reduce the effective voltage) . . . You're trying to
trick me!

The 50% isn't going to work because you have a 2.2K and 2K charging
the timing cap but only a 2K discharging the cap (it charges from the
power supply rail and discharges via pin 7 to ground) For close to
50% you'd make the 2K an order of magnitude larger than the 2.2K
connected to the supply so charge and discharge times are similar. If
you just increased the 2K to say 200K, your cap would probably need to
be smaller to keep the motor from turning on and off visibly.

You can't really reduce the 2.2K to achieve the same thing - it is
logical all right, but then you're asking pin 7 to sink more current
(so keep that at 2.2K or higher)

 

[default]

Better would be this:

+6 ----+------+----[Inductor]---+-----+
| | | |
[C1] [555 & Leds] [C2] [555 PWM]--motor
| | | |
Gnd----+------+-----------------+-----+

In other words, keep the 4 cell supply and the existing
555/transistor/LED circuit. Add the recommended capacitor
at C1. (It connects from pin 8 of the 555 to pin 4 of the
555.) Build the 555 PWM/transistor circuit. Add the recommended
inductor. Add another cap as shown at C2 (again, connects from
pin 8 to pin 4). Don't forget the diode in parallel with
the motor, with the banded end to the + side.

On the each 555, be sure to add a .01 uF cap from pin
5 to ground.

Well, I'd make one or more changes to that. You show the motor
current in the same line with the LED driver. The inductor should
connect back directly to the battery. Ditto the ground wire - just
good RFI practice.

And I'd use a forward biased diode to isolate the LED driver from the
battery if the motor can pull lots of current (like when it starts or
encounters a heavy load) Four AA cells have a relatively high
resistance so may not supply all the current the motor wants without
allowing the voltage to droop.

Putting a diode and large electrolytic on the 555 will keep the 555
happy (for a time) if the motor try's to pull the voltage down.

I'm running a pair of servo motors on a pan and tilt camera from a
supply that is common to the op amps used to drive the motors - the
diode isolation worked wonders since the servos were always starting
from a stop and would suck down the 12 volt 1 amp power supply to 9
volts briefly. Even though the motors only used 100 ma.

 

[default]

Two other things you left out the connection between pin four and the
positive supply rail, both drawings, and it is good practice to put a
cap between pin five and ground to keep the timing stable

 

[randomname]

OK everyone, thanks so much for your input. I've put in so many hours
to this project and just want to see it finished. You all are a great
help.



So as I understand, here's what needs to be modified from the
schematics (please let me know if anything is wrong):

- I'm going to keep the power supply at 4x AA batteries, since the 555s
require 4.5v.
- I will add .01uF caps on each 555 going from pin 5 to ground (I still
don't get what this does.. won't the capacitor just charge up and then
sit there charged?)
- The diode parallel to the motor will be an n4001, (is this the
correct diode?)
- Change the resistor values on the 555 timer that controls the motor
to represent about 40% duty cycle at 100Hz [I'll experiment with this
to find correct values]. Read below to see why 40%.



And here are things I'm not sure about:

- Adding a 100uH inductor where? From + rail to the joint just above
the motor?
- Adding diodes to the 555 timers. From + rail to pin 1? n4001?
- Connecting pin 4 to +. Whats the advantage?



More about the 3v motor: When connected purely to 2 C batteries (as it
was designed to do), it pumps a small stream of water about a foot up.
However, this stream of water is too much for what I need it for... my
specs call for an even tinier stream of water. Ideally, I'd like to be
able to control how much water is flowing, which is why I'm opting for
the PWM solution, so I can effectively control the voltage, and as a
bonus get to use another potentiometer that controls something. Since
3v is too much, I'd like to try around 2 - 2.8 volts, just enough to
barely pump the water up. So I'm thinking roughly 40% duty cycle should
do it.

I just purchased an assortment of diodes and a couple .01uF caps, so
I'm all set except for the inductor, which I'm hoping won't be needed
since I don't understand where to put it and what it would do. I will
put together everything tonight and post results.

Again, thanks a lot everyone (especially Default)

-Sam

 

[default]

OK everyone, thanks so much for your input. I've put in so many hours
to this project and just want to see it finished. You all are a great
help.



So as I understand, here's what needs to be modified from the
schematics (please let me know if anything is wrong):

- I'm going to keep the power supply at 4x AA batteries, since the 555s
require 4.5v.
- I will add .01uF caps on each 555 going from pin 5 to ground (I still
don't get what this does.. won't the capacitor just charge up and then
sit there charged?)

Yes it just sits there charged. Its function is internal to the 555
and it stabilizes the control voltage to the internal comparators
(hopefully preventing them from changing - more useful in electrical
noise rejection then wholesale power supply voltage droop).

You should really read up on the 555 so you understand exactly how it
achieves oscillation - it is hard to get this stuff to work by just
wiring and hoping.

- The diode parallel to the motor will be an n4001, (is this the
correct diode?)

That is good enough for most purposes

- Change the resistor values on the 555 timer that controls the motor
to represent about 40% duty cycle at 100Hz [I'll experiment with this
to find correct values]. Read below to see why 40%.



And here are things I'm not sure about:

- Adding a 100uH inductor where? From + rail to the joint just above
the motor?

Noise rejection components do the most good when physically close to
the source of the noise - otherwise the length of wire between the
filters and noise source act as antenna and radiate noise.

- Adding diodes to the 555 timers. From + rail to pin 1? n4001?

That will help if used with a large value electrolytic cap to
stabilize the voltage to the 555. A cap between pin one and pin
eight. That will see that the 555 has a stable power supply to pull
from when the rest of the circuit is noisy.

- Connecting pin 4 to +. Whats the advantage?

It is just done that way in the typical oscillator application of the
555. It is to reset the 555 in other timing applications - for
instance you have a 5 minute delay but some other requirement demands
that the 555 stop its timing in mid cycle then that pin is grounded.
It should be tied to the positive supply rail to ensure that it isn't
reset - not tied to anything is just not good practice and many 555's
won't work with it floating. Tie pin four and eight together and to
the positive supply.

More about the 3v motor: When connected purely to 2 C batteries (as it
was designed to do), it pumps a small stream of water about a foot up.
However, this stream of water is too much for what I need it for... my
specs call for an even tinier stream of water. Ideally, I'd like to be
able to control how much water is flowing, which is why I'm opting for
the PWM solution, so I can effectively control the voltage, and as a
bonus get to use another potentiometer that controls something. Since
3v is too much, I'd like to try around 2 - 2.8 volts, just enough to
barely pump the water up. So I'm thinking roughly 40% duty cycle should
do it.
OK

I just purchased an assortment of diodes and a couple .01uF caps, so
I'm all set except for the inductor, which I'm hoping won't be needed
since I don't understand where to put it and what it would do. I will
put together everything tonight and post results.

An inductor opposes the rapid change of voltage in this application.
When current flows through an inductor it builds up a magnetic field
around it, when the current tries to increase or decrease the inductor
opposes these changes by taking or adding energy to the magnetic
field. Electrical noise, like what may be causing problems in your
circuit is rapidly changing voltage/current imposed on a power supply
wire where there should just be a steady voltage - the noise plays
havoc with timing.

Again, thanks a lot everyone (especially Default)

-Sam

Let us know how you do, and good luck.

 

[John Fields]

OK everyone, thanks so much for your input. I've put in so many hours
to this project and just want to see it finished. You all are a great
help.



So as I understand, here's what needs to be modified from the
schematics (please let me know if anything is wrong):

- I'm going to keep the power supply at 4x AA batteries, since the 555s
require 4.5v.
- I will add .01uF caps on each 555 going from pin 5 to ground (I still
don't get what this does.. won't the capacitor just charge up and then
sit there charged?)

---
Yes.

Basically, what that input is used for is to vary the period (or
frequency) of the output by changing the voltage on that input. If
that input isn't going to be used its an arguably good idea to
decouple it so that noise won't cause jitter in the timer's output.
---

- The diode parallel to the motor will be an n4001, (is this the
correct diode?)
---
1N4001
---

- Change the resistor values on the 555 timer that controls the motor
to represent about 40% duty cycle at 100Hz [I'll experiment with this
to find correct values]. Read below to see why 40%.



And here are things I'm not sure about:

- Adding a 100uH inductor where? From + rail to the joint just above
the motor?

---
Shouldn't need it.
---

- Adding diodes to the 555 timers. From + rail to pin 1?

---
No, like this: (View in courier)

+6V
+------+ |
+6V>--+--[1N4001>]--+------|Vcc | [LED]
| |+ | | |K
| [1000µF] | OUT|----+
| | | |
GND>--|-------------+------|GND |
| +------+
|
|
+--------------------------------------+
| |
| +----+----+
| | |
| [1N4001] [MOTOR]
| | |
| +------+ +----+----+
+6V>--+--[1N4001>]--+------|Vcc | |
|+ | | C
[1000µF] | OUT|---[R]--B
| | | E
GND>----------------+------|GND | |
+------+ GND


The rationale for the diodes is to isolate the timers from the
voltage drop the motor might cause by having a little supply to keep
them going until the motor turns off.

Note that the 1000µF caps charge up through the diodes, and if the
motor current causes the battery voltage to drop the caps will
supply current into the timers for a while...

 

[ehsjr]

OK everyone, thanks so much for your input. I've put in so many hours
to this project and just want to see it finished. You all are a great
help.



So as I understand, here's what needs to be modified from the
schematics (please let me know if anything is wrong):

- I'm going to keep the power supply at 4x AA batteries, since the 555s
require 4.5v.
- I will add .01uF caps on each 555 going from pin 5 to ground (I still
don't get what this does.. won't the capacitor just charge up and then
sit there charged?)
- The diode parallel to the motor will be an n4001, (is this the
correct diode?)
- Change the resistor values on the 555 timer that controls the motor
to represent about 40% duty cycle at 100Hz [I'll experiment with this
to find correct values]. Read below to see why 40%.



And here are things I'm not sure about:

- Adding a 100uH inductor where? From + rail to the joint just above
the motor?
- Adding diodes to the 555 timers. From + rail to pin 1? n4001?
- Connecting pin 4 to +. Whats the advantage?



More about the 3v motor: When connected purely to 2 C batteries (as it
was designed to do), it pumps a small stream of water about a foot up.
However, this stream of water is too much for what I need it for... my
specs call for an even tinier stream of water. Ideally, I'd like to be
able to control how much water is flowing, which is why I'm opting for
the PWM solution, so I can effectively control the voltage, and as a
bonus get to use another potentiometer that controls something. Since
3v is too much, I'd like to try around 2 - 2.8 volts, just enough to
barely pump the water up. So I'm thinking roughly 40% duty cycle should
do it.

I just purchased an assortment of diodes and a couple .01uF caps, so
I'm all set except for the inductor, which I'm hoping won't be needed
since I don't understand where to put it and what it would do. I will
put together everything tonight and post results.

Again, thanks a lot everyone (especially Default)

-Sam

Here's a simple PWM circuit to control your motor:

View in fixed font:

+6 ---+------------------------------------------+
a| |
[D1] |
| |
+------+----+---------+ +-----+
| | | | | |
| [1K] | ---------- [D3] [Motor]
| | | | 8 | a| |
| | +----|4 | | |
| / | | +-----+
| 25K \<---+----|7 555 | |
| / | | | /
| | a| | 3|---[100R]---| TIP31
| [1K] [D2] | | \ e
| | | | | |
| +----+----|6 | |
| | | | | |
| | +----|2 5|----+ | Diodes: 1N4001
| + | | | | | banded end is
[C1] [C2] ---------- [C3] | cathode; anode
|1000 | .1uF | .01uF | end marked with
| uF | | | a on this
Gnd --+------+-------------------------+---------+ drawing

There are more complicated PWM circuits, but this
simple one should do what you need.
Parts: 2 1K resistors, 1 100 ohm resistor
1 25K potientiometer,
1 1000 uF 16 volt electrolytic capacitor,
1 .1 uF capacitor, 1 .01 uF capacitor
3 1N4001 diodes, 1 555 timer, 1 TIP31 transistor

Build this circuit and connect it to the 6 V battery
source by itself. Be sure to observe the polarity of
the diodes and C1. Test it to make sure you can get
the correct flow rate from the pump. Once you have
it set up properly, then you can connect your the
other 555/transistor/LED circuit. Don't forget to
add the recommended capacitor & diode to your
555/transistor/LED circuit, per the diagram John Fields
provided. They are already added to the PWM circuit
in this post.

Ed

 

[randomname]

Alright, here's a quick update:

I redid my breadboard and have finished the 555 timer for the LEDs, and
just finished the 555 timer for the motor. It's the circuit from this
page http://www.doctronics.co.uk/555.htm under the heading "extended
duty cycle astable." It's just easier for me this way and I don't have
all the parts for a PWM circuit.

Anyway both circuits are working.. I tested the duty cycle of the motor
timer by waving the breadboard and comparing the streaks of when the
LED is on to when it is off. However, the motor will not start through
the TIP31, which could be for a variety of reasons... but I think I
narrowed it down.

I'm having a problem with the TIP31, it doesn't seem to allow enough
current through to get the motor started. Consider this circuit (wire
is =):

+===2.2k====TIP31BASE [set TIP31 to always be on]
+===MOTOR===TIP31COLLECTOR
TIP31EMITTER===== -

The motor will not start, but the TIP31 will get hot.

Do I need a different transistor?

Thanks,
-Sam

 

[randomname]

Here's a simple PWM circuit to control your motor:

View in fixed font:

+6 ---+------------------------------------------+
a| |
[D1] |
| |
+------+----+---------+ +-----+
| | | | | |
| [1K] | ---------- [D3] [Motor]
| | | | 8 | a| |
| | +----|4 | | |
| / | | +-----+
| 25K \<---+----|7 555 | |
| / | | | /
| | a| | 3|---[100R]---| TIP31
| [1K] [D2] | | \ e
| | | | | |
| +----+----|6 | |
| | | | | |
| | +----|2 5|----+ | Diodes: 1N4001
| + | | | | | banded end is
[C1] [C2] ---------- [C3] | cathode; anode
|1000 | .1uF | .01uF | end marked with
| uF | | | a on this
Gnd --+------+-------------------------+---------+ drawing

There are more complicated PWM circuits, but this
simple one should do what you need.
Parts: 2 1K resistors, 1 100 ohm resistor
1 25K potientiometer,
1 1000 uF 16 volt electrolytic capacitor,
1 .1 uF capacitor, 1 .01 uF capacitor
3 1N4001 diodes, 1 555 timer, 1 TIP31 transistor

Build this circuit and connect it to the 6 V battery
source by itself. Be sure to observe the polarity of
the diodes and C1. Test it to make sure you can get
the correct flow rate from the pump. Once you have
it set up properly, then you can connect your the
other 555/transistor/LED circuit. Don't forget to
add the recommended capacitor & diode to your
555/transistor/LED circuit, per the diagram John Fields
provided. They are already added to the PWM circuit
in this post.

Ed

This is the same circuit as I linked to in my previous post, minus the
voltage protection. Am I correct? If so, I'm glad I'm on the right
track Thanks again for your help!

-sam

 

[randomname]

Alright, here's a quick update:

I redid my breadboard and have finished the 555 timer for the LEDs, and
just finished the 555 timer for the motor. It's the circuit from this
page http://www.doctronics.co.uk/555.htm under the heading "extended
duty cycle astable." It's just easier for me this way and I don't have
all the parts for a PWM circuit.

Anyway both circuits are working.. I tested the duty cycle of the motor
timer by waving the breadboard and comparing the streaks of when the
LED is on to when it is off. However, the motor will not start through
the TIP31, which could be for a variety of reasons... but I think I
narrowed it down.

I'm having a problem with the TIP31, it doesn't seem to allow enough
current through to get the motor started. Consider this circuit (wire
is =):

+===2.2k====TIP31BASE [set TIP31 to always be on]
+===MOTOR===TIP31COLLECTOR
TIP31EMITTER===== -

The motor will not start, but the TIP31 will get hot.

Do I need a different transistor?

Thanks,
-Sam

OK, I solved this one.. the resistance to the transistor was too much,
so it was only partly on.

-Sam