stickyfox
Key Veteran
Location: Troy, NY, US
| You're correct; you can vary either R2 or R3 to change the alarm voltage, as it's the ratio that's important. Since R3 is a small value, changing it can make the voltage jump by quite a bit. You might get finer adjustments by changing R2 instead. That was my rationale behind suggesting R2.
If you can't get a 5k pot, you can use either a 10k or 1k pot. Since the ratio is what you're looking out for, you can match any size pot with the the right size fixed resistor. If you use a 1k, I'd recommend replacing R3 with the pot and using the stock value of 2k or 2.2k for R2. That will put 200 ohms somewhere in the middle of your adjustment range. Likewise, a 10k pot should be used to replace R2.
I would not recommend using any larger than a 10k pot, as the circuit depends on current flow through the divider. Too big a value will limit the amount of current available to the circuit. And since we're on the subject, you should not use too small a pot, like a 50 or 20 ohm, as the total current draw will cause the pot to heat up.
-fox |
