I have a (well 8) device that I am controlling by whether or not two of its pins are connected to each other, with 1k ohm resistance between the two.
I set up with PNP transistors, very simple circuit, eight pins to eight transistors, with a common ground, resistor between base pin and microcontroller each. Oh and the 1k resistor inline on the collector to make the device happy.
Seems to work fine except my multi meter reads 1.5k ohm on each enabled pin! where is the 1.5k coming from? oh and that is one direction, the other reads 0.5k - what gives? i thought it would be the same in each direction. is the transistor contributing/taking away resistance?
How are you measuring the "resistance"? Are you simply using a multimeter? Multimeters measure resistance by applying a small voltage to the circuit and actually measure the current that flows.
Once you add transistors to a circuit the current in such a test is no longer just dependent on resistance. Transistors will essentially behave like a pair of diodes. Since diodes have a specific forward voltage, the amount of current they draw is not linear so the concept of "resistance" is not a fixed value.