Hi
Anyone tried using a DS1267 digital pot? I'm experimenting with one, driving it with a PIC16F628. The problem is, moment the chip is powered, the resistance value goes haywire. Even the end to end resistance is nowhere near the actual (100K). It fluctuates between 20k and 30k. With the power off, the end to end resistance shows 98.2K. I'm doing the measurements with a DMM.
Hari
Anyone tried using a DS1267 digital pot? I'm experimenting with one, driving it with a PIC16F628. The problem is, moment the chip is powered, the resistance value goes haywire. Even the end to end resistance is nowhere near the actual (100K). It fluctuates between 20k and 30k. With the power off, the end to end resistance shows 98.2K. I'm doing the measurements with a DMM.
Hari
I haven't tried this chip, but the behaviour you describe is odd.
Things to try:
Check the supply voltage is correct and not noisy.
Check that $RST$ is tied low.
Check that the DMM is not misbehaving. Try another meter, preferably a conventional one.
Check that you're actually measuring across the correct pins. Looking at the block diagram the end-end resistance should be unaffected by the supply voltage, so there's got to be something odd going on.
w
Things to try:
Check the supply voltage is correct and not noisy.
Check that $RST$ is tied low.
Check that the DMM is not misbehaving. Try another meter, preferably a conventional one.
Check that you're actually measuring across the correct pins. Looking at the block diagram the end-end resistance should be unaffected by the supply voltage, so there's got to be something odd going on.
w
OK, I would try clocking a value into the shift register using switches.
The wiper value should be 50% on power-up, so this is a last resort.
You need 3 switches. Pull RST, CLK & DQ down to ground using resistors, say 5k. Connect the switches to +VCC and the I/O pins so that you can control the state of the pins using the switches.
Set RST low, CLK high and DQ to high or low as you choose.
Set RST high and toggle CLK low then high. Repeat 16 times, setting a value for DQ as you choose, until you have clocked 17 values into the shift register. (Could be all '1's.) Set RST low.
Try measuring the end-to-end and wiper resistances again. If this fails, then the chips are faulty, for whatever reason.
w
The wiper value should be 50% on power-up, so this is a last resort.
You need 3 switches. Pull RST, CLK & DQ down to ground using resistors, say 5k. Connect the switches to +VCC and the I/O pins so that you can control the state of the pins using the switches.
Set RST low, CLK high and DQ to high or low as you choose.
Set RST high and toggle CLK low then high. Repeat 16 times, setting a value for DQ as you choose, until you have clocked 17 values into the shift register. (Could be all '1's.) Set RST low.
Try measuring the end-to-end and wiper resistances again. If this fails, then the chips are faulty, for whatever reason.
w
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