On the topic of circuit bending...how does a potentiometer work with a trimmer?

Question

Basically, I have a 500K potentiometer and the circuit crashes when the pot is turned all the way to either end. Anyone know what size trimmer to install? I know essentially how it works but don't know what size to buy.

Answer 1

ANY pot will have the same problem. Your problem is a design problem and must be remedied by installing limiting resistors.

Lets say you hook up your 500K pot to a 12 Volt battery, on end to +, the other end to -, with the center wiper attached to a meter, and the other end of the meter attached to - of the battery. As you adjust the pot, you will see from 0.0 to 12.0 Volts depending on where you adjust the pot. If the design can not handle 0.0 or 12.0 volts, and I want my design to be idiot proof, then I need to add limiting resistors. I can do this by design, guess or measurement. Lets say I figure out that any voltage below 1.0 volts, and above 11.0 volts causes a problem, so I want to design my circuit so the output of the pot will never go below 1.0V or above 11.0V.

Using Ohms law (e/i=r), I can figure out that 12V divided by 500K = 24 uA. This is the current going thru the pot all the time. 1.0V/24uA = 41.6K Ohms, which is voltage difference I want to remove from the circuit on both ends. This is the size of the voltage limiting resistor, which I'll round to 42K Ohms.

So if we go back to our battery and pot, and add a 42K ohm resistor between the + of the battery and the pot, and another 42K ohm resistor between the - and the pot, this will acomplish what we want. Now as you adjust the pot, you will only see from 1.0 to 11.0 volts at the meter.

You need to extrapolate this to your circuit. Find out why out what values it doesn't like, and add limiting resistors. If I knew more about what you were adjusting I could tell you more