Since all you want to do is drive a low impedance load using PWM, why not use a simple FET driver circuit as per this arduino tutorialhttp://www.arduino.cc/playground/Learning/SolenoidTutorial
How about an opamp buffer? Just wired as a voltage follower so you'll have 1M impedance to the opamp and depending which one you pick you will have a decent enough voltage source
I must be doing something wrong. I wired up the op amp as a voltage follower, and used it with the potentiometer wired up as a voltage divider. I get from 0 Volts to 5 Volts coming out of the potentiometer into the + input of the op amp. But I get .3 Volts to 4.3 Volts coming out of the op amp when I leave the output floating. When I hook up the output of the op amp to the low impedance device input, I get only .3 Volts to 2.5 Volts output. UPDATE: I should clarify that I am just using a + 5 Volts power source for now. So the 0 to 5 Volts that comes out of the potentiometer is correct. But the output of the op amp has a reduced range, although it seems to vary correctly within that range, smoothly without any jumps.That is normal behavior for many op-amps (esp older types) unless you obtain one that is specified to have 'rail to rail' output voltage capability. So check the datasheet for your specific op-amp type to see what it's output voltage swing spec is.Lefty
That is normal behavior for many op-amps (esp older types) unless you obtain one that is specified to have 'rail to rail' output voltage capability. So check the datasheet for your specific op-amp type to see what it's output voltage swing spec is.Lefty
Ah, thought it was good, but looked closer and its not rail to rail and also only has 35ma output max so doesn't help much
Most op-amp aren't designed to supply much output current, 35ma is probably pretty typical. Most circuits needing more current drive from an op-amp stage just wire in a transistor as a voltage follower that can supply higher output current. There are special op-amps designed with higher output current capability but you will pay a premium for it compared to more standard op-amps.Lefty
Quote from: MarkT on Jul 28, 2012, 03:21 amWhat is the load?I need to send a signal of between 0 and 12 Volt to an electric-over-hydraulic trailer brake.
What is the load?
You seem to be making hard work out of this project.
You can drive an open collector transistor or FET from the arduino. Your 50ohms load is connected between your 12 volt supply rail and the collector of the transistor.
If there's a datasheet for the device it would be really re-assuring to see it - I don't know how such a thing works and what sort of frequencies of PWM are suitable.
Also automotive devices often are permanently connected to the chassis/ground and can only be switched on the high-side - if this is so you'll need a PNP or p-channel device to switch and some kind of level-shifting circuit to control this from the Arduino.
I can't do that because I only have one wire that goes to my "load." Not two.
QuoteI can't do that because I only have one wire that goes to my "load." Not two. No you always have two wires to connect to the load otherwise you can't get any current to flow.Your other "hidden" wire is either the ground or the +ve power supply.What do you need to do wit this wire to turn it on. If it is supply +ve then the ground is your other control wire.