- Wed Oct 07, 2015 2:40 pm
#185099
This is potentially (probably?) a really dumb question, but I am a software engineer who is working with electronics for the first time so my apologies in advance. Hopefully someone will take pity on a noob.
Unnecessary Background: This is a Raspberry Pi project using Cat6 Cabling to link a PCB that has the CD74HC4067 multiplexor breakout. Eventually I will have up to 16 contact switches connected to the 16 channels on the MUX. The setup works well, my switches work well and provide +3.3V to a channel when closed. I can read from any channel just fine.
Here is my question:
I want to light up an LED when the mux is reading an individual channel, but I cannot seem to get it to work. I have the LED in series with a channel (any of the 16), along with a 200 OHM resistor. I can still read the channel when power is applied, but the LED never lights. I have tried 9 different LED colors in 3 different sizes and powers, but nothing changes. I test each of the LEDs individually buy connecting it to ground (but still past the resistor) when +3.3V is supplied and all of them light up, to different brightness. Hook the same lead of the LED to the MUX channel and no light, but the channel does show high (power applied) when read, and I get 3.2V if I test with a multimeter from the signal pin to ground.
This should be a very simple circuit, the multiplexer is supposed to be passing whatever the supply voltage and current are. within its specs which are much wider than I am providing. Does the chip drop current so much that the LED can't light but can still pass power?
I have tested with three different identical mux breakouts (Sparkfun rocks!), each of them soldered to pins which are soldered to RJ45 Breakouts, with the channel I am testing soldered at both ends (mux side and LED side). All three mux boards do exactly the same thing.
If I place an identical LED (same size color and even batch) to the one I am testing between the SIGnal pin and ground it will light, which should mean that there is enough power coming through the switch, right?
Am I overlooking something obvious? I am sure I am but for the life of me I can't figure out what! Too bad I can't debug this the same way I can with the python code that drives it.
Thank you in advance for any insight you can provide.
-M Matrix.
Unnecessary Background: This is a Raspberry Pi project using Cat6 Cabling to link a PCB that has the CD74HC4067 multiplexor breakout. Eventually I will have up to 16 contact switches connected to the 16 channels on the MUX. The setup works well, my switches work well and provide +3.3V to a channel when closed. I can read from any channel just fine.
Here is my question:
I want to light up an LED when the mux is reading an individual channel, but I cannot seem to get it to work. I have the LED in series with a channel (any of the 16), along with a 200 OHM resistor. I can still read the channel when power is applied, but the LED never lights. I have tried 9 different LED colors in 3 different sizes and powers, but nothing changes. I test each of the LEDs individually buy connecting it to ground (but still past the resistor) when +3.3V is supplied and all of them light up, to different brightness. Hook the same lead of the LED to the MUX channel and no light, but the channel does show high (power applied) when read, and I get 3.2V if I test with a multimeter from the signal pin to ground.
This should be a very simple circuit, the multiplexer is supposed to be passing whatever the supply voltage and current are. within its specs which are much wider than I am providing. Does the chip drop current so much that the LED can't light but can still pass power?
I have tested with three different identical mux breakouts (Sparkfun rocks!), each of them soldered to pins which are soldered to RJ45 Breakouts, with the channel I am testing soldered at both ends (mux side and LED side). All three mux boards do exactly the same thing.
If I place an identical LED (same size color and even batch) to the one I am testing between the SIGnal pin and ground it will light, which should mean that there is enough power coming through the switch, right?
Am I overlooking something obvious? I am sure I am but for the life of me I can't figure out what! Too bad I can't debug this the same way I can with the python code that drives it.
Thank you in advance for any insight you can provide.
-M Matrix.