Digital resistor/opto coupler

[Lyndon]

Hi guys,

I have a microcontroller board that has a variable analog voltage
output via a DAC. I want to use this variable voltage to control a
potentiometer on another board. Is there any device that allows me to
run the analog voltage output through two pins and get a variable
resistance through another two pins?

+ DAC output ----- ------ + variable 5k resitance
| |
| |
O O
| |
| |
- DAC output ----- ------ - variable 5k resistance

Thanks guys.

Regards,
Lyndon.

 

[Ken Taylor]

"Lyndon" <webster@netlink.net.au> wrote in message
news:6864d8ba.0406141808.17c58290@posting.google.com...

Hi guys,

I have a microcontroller board that has a variable analog voltage
output via a DAC. I want to use this variable voltage to control a
potentiometer on another board. Is there any device that allows me to
run the analog voltage output through two pins and get a variable
resistance through another two pins?

+ DAC output ----- ------ + variable 5k resitance
| |
| |
O O
| |
| |
- DAC output ----- ------ - variable 5k resistance

Thanks guys.

Regards,
Lyndon.

Are you stuck with using the DAC output? There's a lot of digital pot's

available which may be a better option.

Ken

 

[mike diack]

On Tue, 15 Jun 2004 16:17:06 +1200, "Ken Taylor" <ken123@xtra.co.nz>
wrote:

"Lyndon" <webster@netlink.net.au> wrote in message
news:6864d8ba.0406141808.17c58290@posting.google.com...
Hi guys,

I have a microcontroller board that has a variable analog voltage
output via a DAC. I want to use this variable voltage to control a
potentiometer on another board. Is there any device that allows me to
run the analog voltage output through two pins and get a variable
resistance through another two pins?

+ DAC output ----- ------ + variable 5k resitance
| |
| |
O O
| |
| |
- DAC output ----- ------ - variable 5k resistance

Thanks guys.

Regards,
Lyndon.

Are you stuck with using the DAC output? There's a lot of digital pot's
available which may be a better option.

Ken


Otherwise you're stuck with Vactrols and opto-fets (not nearly as

linear as digital pots, but they ARE isolated).
M

 

[Johnny]

On 14 Jun 2004 19:08:15 -0700, webster@netlink.net.au (Lyndon) wrote:

Hi guys,

I have a microcontroller board that has a variable analog voltage
output via a DAC. I want to use this variable voltage to control a
potentiometer on another board. Is there any device that allows me to
run the analog voltage output through two pins and get a variable
resistance through another two pins?

+ DAC output ----- ------ + variable 5k resitance
| |
| |
O O
| |
| |
- DAC output ----- ------ - variable 5k resistance

Thanks guys.

Regards,
Lyndon.

You could use a PWM output driving a opto-coupler, assuming you have a
supply voltage on the isolated side. You will need to use a
high-speed opto such as H11L1. If you use a low-pass filter on the
output side of the opto coupler, you can get a analogue voltage
output. Variable resistance is more difficult.

regards,
Johnny.

 

On 14 Jun 2004 19:08:15 -0700, webster@netlink.net.au (Lyndon) wrote:

Hi guys,

I have a microcontroller board that has a variable analog voltage
output via a DAC. I want to use this variable voltage to control a
potentiometer on another board. Is there any device that allows me to
run the analog voltage output through two pins and get a variable
resistance through another two pins?

+ DAC output ----- ------ + variable 5k resitance
| |
| |
O O
| |
| |
- DAC output ----- ------ - variable 5k resistance

Thanks guys.

Regards,
Lyndon.

There are a number of other ways of controlling a variable resistance
from a digital signal. Check out Analog Devices TrimDACs, Xicor also
have a range of digital pots. If you want to control the volume of
an audio preamplifier, you could use TI's PGA2311.
You could also use the output of the DAC to control a FET.

 

[Paul Bealing]

Lyndon wrote:

Hi guys,

I have a microcontroller board that has a variable analog voltage
output via a DAC. I want to use this variable voltage to control a
potentiometer on another board. Is there any device that allows me to
run the analog voltage output through two pins and get a variable
resistance through another two pins?

+ DAC output ----- ------ + variable 5k resitance
| |
| |
O O
| |
| |
- DAC output ----- ------ - variable 5k resistance

Thanks guys.

Regards,
Lyndon.

Hello

I built something a few years ago for a specific HVAC application which
provided a isolated 0-100 ohm output of 256 steps form a 0-10 volt input.
It was reasonably simple. The input signal changed little and
infrequently so we used miniature relays to drive a precision resistor
network. A small micro with ADC read the input voltage and used a lookup
table and some calculations to adjust the curve before driving the relays.

There may still be a few suppliers selling these off the shelf.

For a higher resistance output you could probably use opto-fets in place
of relays.

Regards
Paul