I need to apply a resistance from 50 ohms to 600 ohms on a line of 12v.
I found I could use a digital potentiometer but I can not find a board/module can handle 12v I only found one for 5v.
So the question is if exist something like that. How to find that.
Thanks a lot four our help.
12V / 50Ohm = 0,24A
12V * 0,24A = 2,88W,
which digital potentiometer able to handle it?
why you think you need to apply a resistance from 50 ohms to 600 ohms on a line of 12v?
For what application?
What is your project?
Thanks.. Tom.. 
A digital pot that will operate with 12V isn't a problem: AD5280 for one. But putting a 50-600 ohm load across a 12V line is a completely different thing. I've never run across a digital pot that comes anywhere near being able to handle that kind of amperage. 5mA is much more common.
It sounds like you need a software controlled power supply.
These are expensive to buy, or difficult to make. You will not find a digital pot that can do this on its own.
If you do find a programmable power supply it will come with its own description of how to control it.
For example I have a Rigol DS1074z, combined Oscilloscope and signal generator. It uses python and the visa_library to control it. This is a widely used protocol for controlling instruments used in industry especially when creating production test rigs.
When I was a Technical Manager, at a consumer electronics company, I had to liaise the test department to make sure what they were making was suitable for my product. They used several programmable power supplies that used the same interface protocol as my oscilloscope.
These production test rigs could cost hundreds of thousands of £ to create, especially when they included spectrum analysers and network analysers.
For completeness here is a script I wrote (in python) that produces a frequency sweep from the signal generator part of my oscilloscope.
#!/usr/bin/python
"""
Make a Rigol DS1074Z-S oscilloscope produce a frequency sweep
By Grumpy Mike April 2014
"""
import numpy
import time
import matplotlib.pyplot as plot
import sys
from pyvisa.vpp43 import visa_library
visa_library.load_library("/Library/Frameworks/Visa.framework/VISA")
import visa
fValues = [1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.3, 2.6, 3.0, 3.5, 4.0,
5.0, 6.0, 7.0, 8.0, 9.0]
maxFn = 16 # number of frequencies in a decade
print "Rigol DS1074Z-S sweep"
# Get the USB device
instruments = visa.get_instruments_list()
usb = filter(lambda x: 'USB' in x, instruments)
print "Scope ",usb
if len(usb) != 1:
print "Can't find scope", instruments
sys.exit(-1)
scope = visa.instrument(usb[0], timeout=20, chunk_size=1024000) # bigger timeout for long mem
def main():
initGen()
sweep(2,20000)
scope.write(":KEY:FORCE")
scope.close()
def sweep(dec, lim) : # starting decade finishing frequency
f = 0
freq = 0
while freq < lim : # 20KHz limit
freq = fValues[f] * (10**dec)
#print freq
setFreq(int(freq))
f += 1
if f >= maxFn :
f = 0
dec += 1 # next decade
time.sleep(1.1)
def setFreq(f):
scope.write(":SOUR1:FREQ:FIX "+str(f))
def initGen():
scope.write(":SOUR1:OUTPUT1:STATE ON") # enable output
scope.write(":SOUR1:OUT1:IMP FIFT") # low impedance output
scope.write(":SOUR1:FUNC:SHAP SIN") # Sin wave
scope.write(":SOUR1:VOLT:LEV:IMM:AMP 2") # output voltage 2V
scope.write(":SOUR1:MOD:STAT OFF") # turn off modulation
if __name__ == '__main__':
main()
1 Like
Your suggestion of a digital pot is not an appropriate approach to the problem. Perhaps if you told us what you are trying to achieve? ie ...
WHY?
why ??
that is what I need. I have a gauge that measures temperature. That gauge works with 12v. and read resistance from 50 to 600 ohms that shows as temperature. I need to imitate a sender/sensor that no longer exist. Please do not tell me to buy another gauge.
it seems is not possible with a standard board right ??
a lot simpler than that.
just to apply a resistance of 50 to 600 ohms to a 12v line
That is all
May be I can make a board with a list of resistances and and send the 12v line trough one of them according to what I need.
Can something like that be done ?
datasheet? link?
Modify a 4-20 mA current loop to 20-240 mA.
Probably not enough compliance with 12V. Wonder what the voltage drop of the meter is?
Switch in/out various resistors?
Yes.
Hi, @sivi1234
So you have an automotive temperature sensor to imitate.
Probably the simplest way.
Tom..
Do you know the resistance of the gauge? You could use a voltage controlled current source or sink.
1 Like
that was my first think but it seems commercial boards does not work with so little resistances
are you talking about modify the gauge ?
question....
can a multiplexer board help me with that ? at least to avoid the transistors ?
How ?
can a multiplexer board help me ? at least to avoid the transistors connecting the resistances to the multiplexer lines ...
No, I was comparing your proposed circuit to something that exists.
It sounds like you are saying that the temperature sensor you have has a variable resistance ranging from 50 to 600 Ohms. Is that correct?
It also appears that the existing gauge acts as an ammeter that displays the current resulting from the temperature sensor.
Draw a diagram of how the existing temperature sensor and gauge are connected including how the 12V is connected. If you have a part number or data sheet for the sensor, post that.