Electrical – Replace Potentiometer With Arduino Controlled Circuit

automationdigital potentiometer

Background:

I recently bought a Scr Voltage Regulator (10000w Ac110v 220v 75a) to act as a motor controller for a hobby project (Figure 1). After taking it apart, I found the Voltage Regulator is controlled by a 220k Ohm 2W Potentiometer (Figure 2).

Figure 1: SCR Voltage Regulator

Figure 2: 220 K ohm 2W Potentiometer

Question:

I'd like to replace the mechanical Potentiometer with a component I can control with a microcontroller. I found the ADN2850 However, this seems like it can only support 1 W.

Is there another type of chip on the market I should be looking at?

How would I build a circuit that allows me to use a smaller control current to regulate the speed regulator?

Best Answer

You can't do this easily and should not attempt it. You could easily hurt yourself or damage your computer.

You need a power controller with a DC voltage input that is isolated from the mains. It's far easier to design something like that from scratch than to try to retrofit to a non-isolated phase control. That pot, for example, will be subject to hundreds of volts in operation, far beyond what any digital pot can withstand.

If you connect your Arduino directly to a non-isolated circuit there's a good chance it will be sitting at 120VAC relative to ground and could electrocute you or blow your PC's motherboard to smithereens via the USB programming port.

Related Solutions

Electronic – How to control X9C102 digitally controlled potentiometer

As a first step, make sure you are measuring what you think you are measuring. Disconnect the wiper from the PIC input pin, in case leakage current from the PIC pin is influencing your measurements.

If this actually is the problem, the normal solution is to drive the load (the PIC input) from a low impedance source, i.e. a buffer amplifier. This would normally be a "rail to rail" opamp (input and output voltages can swing to the supply rails) wired in unity gain configuration.

But also check that the PIC software is setting that pin up correctly as an input! Looking at the PIC datasheet (pin 165) the "analog voltage source" should have an impedance < 10k. The X9C102 already does, (it's range is up to 1k) so your original configuration ought to work!

Try pulling the PIC pin high or low with a 1k resistor; if it doesn't swing very close to the supplies, you either have a software configuration problem (the pin is still an output) or possibly a damaged PIC. At a glance your software looks OK but I'm not familiar with that PIC.

MAX5483, 10-bit digital potentiometer controlled via SPI by arduino

Try this. All I need was just rewrite the byte0 and byte1, added a delay after CS goes low and before CS goes high. Also I changed the order of the SPI.transfer() so that its COMMAND, BYTE 1, and then BYTE 0.

void digitalPotWrite(int value) {
digitalWrite(csPin, LOW);
//some delay here delay(1) ?
byte command=0x0;
byte byte0 = (value & 0x03) << 6;
byte byte1 = (value & 0x3FC) >> 2;
SPI.transfer(command);
SPI.transfer(byte1);
SPI.transfer(byte0);
//some delay here delay(1) ?
digitalWrite(csPin, HIGH);
}

If this doesnt work, then add this to your setup.

SPI.setDataMode(SPI_MODE2);

Looking at the page 15, it seems that the clock base rests at '1'. And the data is captured on the clocks rising edge. I'm not sure what the default setting is for SPI.begin() but it could be that its set for SPI_MODE1 (just a guess).

Have a look at SPI for the different modes and what they mean.