Newbie: Simple amplifier and voltage to current converter

[[email protected]]

Hi everybody

I new to electronics and I need your help. I am experimenting with a
microcontroler and I want a 0-5V output to make it 0-10Volt....can
you tell me where I can find a simple circuit to implement?

Another option is to covert the 0-5V to4-20mA. Can I do it in a
simple way?

Thank you

Harry

 

[Rich Webb]

Hi everybody

I new to electronics and I need your help. I am experimenting with a
microcontroler and I want a 0-5V output to make it 0-10Volt....can
you tell me where I can find a simple circuit to implement?

Part of the answer depends on how much current you'll be switching on
the 10V side. Another part on how quickly (and how often) you'll need to
operate it.

A simple, reliable approach is to have the microcontroller I/O pin drive
a transistor switch that in turn controls a relay. If the current's
you're switching are low enough (and you can accommodate a small voltage
drop) you could switch the load directly with a transistor or pair of
transistors.

Also, on the "make 10 volt" question, do you also need to create a 10V
source from 5 VDC?

 

[Chris]

Hi everybody

I new to electronics and I need your help. I am experimenting with a
microcontroler and I want a 0-5V output to make it 0-10Volt....can
you tell me where I can find a simple circuit to implement?

Another option is to covert the 0-5V to4-20mA. Can I do it in a
simple way?

Thank you

Harry

If you've got a 0-5V output and a 12VDC supply, it's easy with an op
amp (view in fixed font or cut&paste to M$ Notepad):

|
| .----------.
| | |
| | |
| | uC | 1/2 LM35
| | |
| | |Analog output +12V
| | | 0-5V |\|
| | o----------------|+\ 0-10V Out
| | | | >---o-------o
| | | .---|-/ |
| | | | |/| .-.
| | | | === | |10K
| | | | GND | |
| | | | '-'
| | | | |
| | | '----------o
| | | |
| | | .-.
| | | | |10K
| '----------' | |
| '-'
| |
| ===
| GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

The simplest way to get a 4-20mA output with a microcontroller is to
make a 0-20mA output:

|
| .----------. +12V
| | | |
| | | '---------o
| | uC | 1/2 LM35
| | | .---------o
| | |Analog out +12V |
| | | 0-5V ___ |\| |
| | o------|___|-o-------|+\ |/
| | | 47K | | >-------| 2N3904
| | | .-. .---|-/ |>
| | | 12K| | | |/| |
| | | | | | === |
| | | '-' | GND |
| | | | | |
| | | === | |
| | | GND '----------------o
| | | |
| | | |
| | | .-.
| '----------' 47| |
| | |
| '-'
| |
| ===
GND
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

This circuit works in a very similar manner to the one above. The 47K
and 12K resistors cut the op amp input to about 0-1VDC. The op amp
raises the output voltage as necessary to achieve that 0-1V across the
47 ohm resistor, which is about 0-20mA. Use 1% resistors for better
precision. If you really need precision, you also might want to
choose a single supply op amp with lower offset voltage. The 7mV max
offset will result in a 14mV max error in the 0-10V, and an 0.15mA
error in the current source.

Also, the current source is compliant to about 10V. If that isn't
enough for the instrument or device you're driving, raise the op amp/
transistor power supply voltage accordingly. But in that case, you'll
need a transistor that can handle more power.

Oh, and since the LM358 has two op amps iin one package, you can do
both at the same time.

Cheers
Chris

 

[Chris]

If you've got a 0-5V output and a 12VDC supply, it's easy with an op
amp (view in fixed font or cut&paste to M$ Notepad):

|
| .----------.
| | |
| | |
| | uC | 1/2 LM35
| | |
| | |Analog output +12V
| | | 0-5V |\|
| | o----------------|+\ 0-10V Out
| | | | >---o-------o
| | | .---|-/ |
| | | | |/| .-.
| | | | === | |10K
| | | | GND | |
| | | | '-'
| | | | |
| | | '----------o
| | | |
| | | .-.
| | | | |10K
| '----------' | |
| '-'
| |
| ===
| GND
(created by AACircuit v1.28.6 beta 04/19/05www.tech-chat.de)

Cheers
Chris

Sorry -- a small tweak. If you're deriving your +5V supply from the
+12V supply (a good idea), or if the +12V supply is turned on first,
the high impedance potential at the uC output pin could see a higher
voltage than the uC power supply, which will cause the uC to latch up
at turnon and possibly damage it. Simple fix:

|
|
| .----------.
| | |
| | |
| | uC | 1/2 LM35
| | |
| | |Analog out +12V
| | | 0-5V |\|
| | o------o---------|+\ 0-10V Out
| | | | | >---o-------o
| | | .-. .---|-/ |
| | | 22K| | | |/| .-.
| | | | | | === | |10K
| | | '-' | GND | |
| | | | | '-'
| | | === | |
| | | GND '----------o
| | | |
| | | .-.
| | | | |10K
| '----------' | |
| '-'
| |
| ===
| GND
|
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Cheers
Chris

 

[Jamie]

Sorry -- a small tweak. If you're deriving your +5V supply from the
+12V supply (a good idea), or if the +12V supply is turned on first,
the high impedance potential at the uC output pin could see a higher
voltage than the uC power supply, which will cause the uC to latch up
at turnon and possibly damage it. Simple fix:

|
|
| .----------.
| | |
| | |
| | uC | 1/2 LM35
| | |
| | |Analog out +12V
| | | 0-5V |\|
| | o------o---------|+\ 0-10V Out
| | | | | >---o-------o
| | | .-. .---|-/ |
| | | 22K| | | |/| .-.
| | | | | | === | |10K
| | | '-' | GND | |
| | | | | '-'
| | | === | |
| | | GND '----------o
| | | |
| | | .-.
| | | | |10K
| '----------' | |
| '-'
| |
| ===
| GND
|
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Cheers
Chris

Ok, Am I the only one having a problem with the above component
being used which is a temperature sensor if I remember ?
LM35 ?
Maybe the OP meant a LM358 ?

 

[Chris]

Ok, Am I the only one having a problem with the above component
being used which is a temperature sensor if I remember ?
LM35 ?
Maybe the OP meant a LM358 ?

Hi, Jamie. The temperature sensors are the 1N4148 diodes, in another
post. The LM358 is a dual single supply op amp, a "jellybean" IC
mentioned in both posts. And yes, the LM35 is a temperature sensor.

Although somewhat dated (it's been around for over 25 years), the
LM358 and LM324 (a quad) are the most common (and probably just about
the cheapest) op amps out there. You can easily get one of either for
$0.12 each or so if you buy by the reel. And the onesie price for the
LM358 in an 8-pin DIP package is $0.21 at Mouser. Two for the price
of a postage stamp. C'mon -- can't beat that.

http://www.national.com/ds.cgi/LM/LM158.pdf
http://www.national.com/ds.cgi/LM/LM124.pdf
http://www.national.com/ds.cgi/LM/LM35.pdf

Cheers
Chris