Mike said:Would micro reed relays be too big?
They would certainly work. I found some that would be suitable- but it would be more expensice than the switch.
Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
Mike said:Would micro reed relays be too big?
ljcox said:You need a configuration that does not include the B - E voltage drops.
I suggest :-
connect the emitter of the PNP to +3.3 V and the emitter of the NPN to gnd.
Now connect a resistor from the base of the PNP to the logic output and a resistor from the base of the NPN to the same point. Connect the 2 collectors together. In this configuration, the only voltage drop will be the saturation voltage which ought to be about 0.2 V is you have enough base current. Note that the circuit will act as an inverter. So you'll have to account for this somewhere.
ljcox said:You need a configuration that does not include the B - E voltage drops.
I suggest :-
connect the emitter of the PNP to +3.3 V and the emitter of the NPN to gnd.
Now connect a resistor from the base of the PNP to the logic output and a resistor from the base of the NPN to the same point. Connect the 2 collectors together. In this configuration, the only voltage drop will be the saturation voltage which ought to be about 0.2 V is you have enough base current. Note that the circuit will act as an inverter. So you'll have to account for this somewhere.
Make sure that the IO port on the PIC is configured as an output ASAP after reset. When the input to this transistor circuit is floating, BOTH transistors are turned on at the same time and a high collector current will flow possibly damaging the transistors. When the PIC is in reset, all IOs are in the high impedance state (floating) so keep the time between reset and setting TRISGPIO to 0 as short as possible.If i make both resistors 100 - transistors nearly burn out.
This is a good point.kchriste said:Make sure that the IO port on the PIC is configured as an output ASAP after reset. When the input to this transistor circuit is floating, BOTH transistors are turned on at the same time and a high collector current will flow possibly damaging the transistors. When the PIC is in reset, all IOs are in the high impedance state (floating) so keep the time between reset and setting TRISGPIO to 0 as short as possible.
That was my first thought.dalmation said:would a 10K pull down resistor connected to the base of the PNP and ground prevent it opening on high z input, without affecting normal operation too much?
Yes & yes.dalmation said: