Hi there. I'm designing a circuit so that I can control 6 switches of a device using transistors and the serial port on my computer. I have 6 data pins going into the base of 6 transistors. The positive end and negative end of each switch is going to each collector and each emitter is going to ground of the serial port. Basically, when the data pin is on the transistor draws current from the device to the ground of the serial port and the switch is off. When the data pin is off the transistor has high impedence so the current goes through the switch instead and it is on.
I have found that this works for just one switch but not when I hook up the others. I have a theory that too much current is being drawn from the device to the ground of my serial port for one switch and not allowing for enough current at the other switches. i tried placing different resistors at the collector of the transistors but i am unsure what values to use and the ones i tried still dont work.
If it helps I know that there are about 3 micro amps going through each switch when it is on. I need to keep the current around this value without adding or drawing too much. I have also heard of relays which would work but I would rather not go that route. Any ideas on what I should do or how I should change my circuit? thanks.
I have found that this works for just one switch but not when I hook up the others. I have a theory that too much current is being drawn from the device to the ground of my serial port for one switch and not allowing for enough current at the other switches. i tried placing different resistors at the collector of the transistors but i am unsure what values to use and the ones i tried still dont work.
If it helps I know that there are about 3 micro amps going through each switch when it is on. I need to keep the current around this value without adding or drawing too much. I have also heard of relays which would work but I would rather not go that route. Any ideas on what I should do or how I should change my circuit? thanks.