Sevro amp schematic

[Pat Ford]

Hi All;
I want to build a circuit that will take a voltage, and drive a geared
motor to a position based on the voltage. Position will be sensed by a pot.
What I cant figure out is the bidirectional drive. I have 12 volts, and I
also have 6 LM18200. Does anyone have a circuit that would work?
Pat

 

[Tim Wescott]

Hi All;
I want to build a circuit that will take a voltage, and drive a geared
motor to a position based on the voltage. Position will be sensed by a pot.
What I cant figure out is the bidirectional drive. I have 12 volts, and I
also have 6 LM18200. Does anyone have a circuit that would work?
Pat

If you drive the whole thing from an AVR or a PIC then your problems are
solved. Not only can you select a device with an ADC and PWM output,
but you can put in the adjustable deadband, velocity limiting and
trapezoidal velocity profiling that you'll find you need to keep the
system stable and working correctly.

If you don't believe me then here's a handy circuit: When Vin > 0 the
4053 switches to the + input and the "DIR" output is on. When Vin < 0
the 4053 switches to the - input and the "DIR" output is off. When Vin
= 0 the DIR output oscillates like crazy and you get all sorts of weird
transients on "MAG" -- but what do you want for free? Figuring out how
to get some hysteresis in the comparator is your problem.
___
.---|___|----.
| |
4053 | Opamp |
___ | |\ |
Vin /o-|___|--o---|-\ | Mag
o---o----o/ | >-----o--------o
| | o--------o---|+/
| | | |/
| | .-.
| | | |
| | | |
| | '-'
| | |
| | |
| | ===
| | GND
| |
| '----------------------.
| |
| Comparator |
| |\ |
'--------------------|+\ | Dir
| >----o---------o
.---|-/
| |/
|
|
===
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

 

[Winfield Hill]

I want to build a circuit that will take a voltage, and drive a
geared motor to a position based on the voltage. Position will be
sensed by a pot. What I cant figure out is the bidirectional drive.
I have 12 volts, and I also have 6 LM18200. Does anyone have a
circuit that would work?

Is that the LMD18200 you're talking about? That's an H-bridge,
which is naturally bi-directional. Have you studied H bridges?
Have you read NSC's an-828 and an-694 application notes?

 

[Pat Ford]

Is that the LMD18200 you're talking about? That's an H-bridge,
which is naturally bi-directional. Have you studied H bridges?
Have you read NSC's an-828 and an-694 application notes?

Thats the one, what I was thinking is have a 555 setup up to do variable
pwm with a null in the center of the input range and a comparitor to detect
direction. Does that sound like a good plan.

The other path is get a small pic, program it to do it all.

 

[Robert Latest]

Thats the one, what I was thinking is have a 555 setup up to do variable
pwm with a null in the center of the input range and a comparitor to detect
direction. Does that sound like a good plan.

No. The 555 (why is everybody so in love with it?) doesn't
naturally lend itself to variable-duty cycle apps. This issue has
been beaten to death recently in another thread in this group.
Use a LM393. Next thing you need to worry about are loop
stability issues.

The other path is get a small pic, program it to do it all.

Not necessarily easier.

robert