Hello there!
I got this old Videomixer lying around here, and i want to substitute all the switches with transisors to be able to control it via arduino.
But what about the potentiometers? How would i mimic one?
I want to be able to control them via Arduino aswell.
Will transistors work?
Thanks in advance
Great Link and resource, thank you Richard!
I will now check out what the Voltage and mode of the pots is.
Just wanted to know if its possible at all before desoldering stuff.
If you mesure the voltage of the potentiometers from down position to up position (0-100%) you can pwm a transistor having that max voltage.
David
I measured the voltage to be 1.3v to 3.65v (0%-100%)
Thanks for the hint ArduinoM
I have standard PNP and NPN transistors lying around here, but i have no clue how to pwm a transisotr to mimic this Voltage range.
Could you shortly explain what you meant?
Thanks so far
Don't think you'll need a transistor for that voltage range. Just a low pass filter and a suitably sized resistor to ensure that it doesn't draw too much from the Arduino
Wouldn't building each lowpass circuit for 8 potentiometers be more complicated as soldering 8 transistors?
I'm not quite sure, just asking.
yea but there 2 different things
you probally wont need a transistor as they are used to switch heavier loads
you would probably need a low pass filter to smooth the pwm pulses to smooth voltage
its kinda like asking "well why wouldn't I fly when I can use a washing machine"
me, I would use digital pots, but that is because I have a few
I got this old Videomixer lying around here,
So do you know that the potentiometers just produce a voltage and don't actually carry signals. They would if it were an audio mixer, in which case just plugging a voltage in, however smooth, will not work.
In hindsight - I'm with Osgeld. That's a perfect application for digital pots. You'll need to confirm Mike's point though.
Right. But he already said ...
Quote:
I measured the voltage to be 1.3v to 3.65v (0%-100%)
Yes but I bet he measured it with a DVM, that doesn't tell the whole tale does it. If it had a video signal on it you would expect to see something on a DVM it's just it wouldn't mean very much.
His application (the video switcher)
I thought it was a Videomixer , mixing and switching are two different things, you don't switch with a slider pot.
Well, if the videosignal goes through the slider, that's whole another matter, then you really need a digital pot.
But if it's just a pot dividing a constant dc, then you can use pwm from the arduino. Read analogWrite() - Arduino Reference
every step from 1-255 represents 0.0196V if you have 5V adruino
[edit]With that voltage level you do not need transistor if the amp level is less than 20-30mA[/edit]
But with videosignal and you have an ordinary pot and a servo, turn the pot with a servo, and videosignal going through the pot
servo controlled by arduino. (digital pot makes more sense and is cheaper)
David
Thnaks for the healthy thread 
It is actually a WJ-AVE3 Videoeffectgenerator, which has the ability to mix two sources. The whole thing is digital, therefor the pots are just generating input signals for the "CPU"
Are digital pots really that expensive? I get one IC here for about 4 dollars?
Grumpy_Mike you are right, i measured with a a DVM, as i already knew the pots don't carry actual signals as opposed to like a audio-mixer.
Just one thing, if you pwm into a digital device, it might not work, so you need to smooth the signal with a small capasitor (small is the keyword)
Grumpy_Mike has a great site that explanes such things
http://www.thebox.myzen.co.uk/Tutorial/PWM.html