reef-pi :: An opensource reef tank controller based on Raspberry Pi.

speedstar · Dec 4, 2018

buddy. said:
I posted this in my build thread but I am just going to post it here for more visibility.

I am testing out my 8 channel 5v relay boards.

First I tested with just the raspberry pi by connecting up the 5v, ground and an outlet GPIO and it worked as expected.

Next I tried with the pi-HAT but it is not activating the relay. The input of the ULN2803 is receiving 3.25v. The ULN2803 is outputting only 0.6v to the relay board.
I tried a different GPIO on the second ULN2803 on the pi-HAT with the exact same result.

The VCC light is on when I connect the relay board to the 5v and GND on the 10pin connector on the pi-HAT.

The ULN inputs have continuity with the GPIO outlets. The ULN outlets also have continuity with the 10pin connector.
The ULN's are also grounded on their number 9 pin and have 5v on their number 10 pin. Measuring the voltage on pin 9 and 10 gives 5v.

Can anyone help me figure out why the ULN2803 output is so low and not activating the relay?

You tested for continuity, but did you also test for shorts between pins. remove the chip and make sure no pin to pin traces are connected. Did you use sockets or chip direct to board?

speedstar · Dec 4, 2018

Sometimes solder blobs can get under the socket, apologies for not knowing your solder skills or electronics

dmolavi · Dec 4, 2018

theatrus said:
I'm interested in the range of the dimmer input. e.g., is it 0-10V? 0-12V? 0-5V? etc. By measuring across the two fixed terminals in the potentiometer we know the full range of the dimmer input.

0-10V nominal.

There is a model of the Ranco that has an analog output for the temp reading (of course, I didn't get that one *facepalm*), but I'm guessing that it can be pulled from something on the PCB in the enclosure...

Ranjib · Dec 4, 2018

buddy. said:
I posted this in my build thread but I am just going to post it here for more visibility.

I am testing out my 8 channel 5v relay boards.

First I tested with just the raspberry pi by connecting up the 5v, ground and an outlet GPIO and it worked as expected.

Next I tried with the pi-HAT but it is not activating the relay. The input of the ULN2803 is receiving 3.25v. The ULN2803 is outputting only 0.6v to the relay board.
I tried a different GPIO on the second ULN2803 on the pi-HAT with the exact same result.

The VCC light is on when I connect the relay board to the 5v and GND on the 10pin connector on the pi-HAT.

The ULN inputs have continuity with the GPIO outlets. The ULN outlets also have continuity with the 10pin connector.
The ULN's are also grounded on their number 9 pin and have 5v on their number 10 pin. Measuring the voltage on pin 9 and 10 gives 5v.

Can anyone help me figure out why the ULN2803 output is so low and not activating the relay?

How you are connecting the ULN2803 output to relays? Remember, ULN2803 is a sink type driver, i.e. individual output pins of ULN2803 will act as GND (not +ve) for relays. So, while testing with multimeter, you should put the +Ve probe on 12V and the -Ve probe in ULN2803a pins.

buddy. · Dec 4, 2018

speedstar said:
You tested for continuity, but did you also test for shorts between pins. remove the chip and make sure no pin to pin traces are connected. Did you use sockets or chip direct to board?

speedstar said:
Sometimes solder blobs can get under the socket, apologies for not knowing your solder skills or electronics

Thanks. I used a socket. I didn't test for shorts but I will do it tonight.

Ranjib said:
How you are connecting the ULN2803 output to relays? Remember, ULN2803 is a sink type driver, i.e. individual output pins of ULN2803 will act as GND (not +ve) for relays. So, while testing with multimeter, you should put the +Ve probe on 12V and the -Ve probe in ULN2803a pins.

The ULN output goes to the 10 pin connector on the pi-hat. So you have 1 5v, 1 ground and then 8 outlets.
I connected the 10pin connector 5v to the VCC on the relay board.
I connected the 10 pin ground to ground on the relay board.
I connected an outlet on the 10 pin to CH1 on the relay board.
When I have the outlet switched off in reef-pi the ULN output reads 0v and when I switch the outlet on the ULN output reads 0.6v. But I was putting the -ve probe to ground and the +ve on the ULN output.

Diamond1 · Dec 4, 2018

buddy. said:
Thanks. I used a socket. I didn't test for shorts but I will do it tonight.

The ULN output goes to the 10 pin connector on the pi-hat. So you have 1 5v, 1 ground and then 8 outlets.
I connected the 10pin connector 5v to the VCC on the relay board.
I connected the 10 pin ground to ground on the relay board.
I connected an outlet on the 10 pin to CH1 on the relay board.
When I have the outlet switched off in reef-pi the ULN output reads 0v and when I switch the outlet on the ULN output reads 0.6v. But I was putting the -ve probe to ground and the +ve on the ULN output.

Might be a stupid question but do you have a 12volt power supply hooked up to the hat when your testing?

buddy. · Dec 4, 2018

Diamond1 said:
Might be a stupid question but do you have a 12volt power supply hooked up to the hat when your testing?

Yep I did but I haven't actually tested it. I thought it was only needed for the dosing pumps though?

speedstar · Dec 4, 2018

buddy. said:
Yep I did but I haven't actually tested it. I thought it was only needed for the dosing pumps though?

correct

also wanted to mention the outputs on/off will be the inverse going through the chip compared to the pi direct.

b4tn · Dec 4, 2018

buddy. said:
I posted this in my build thread but I am just going to post it here for more visibility.

I am testing out my 8 channel 5v relay boards.

First I tested with just the raspberry pi by connecting up the 5v, ground and an outlet GPIO and it worked as expected.

Next I tried with the pi-HAT but it is not activating the relay. The input of the ULN2803 is receiving 3.25v. The ULN2803 is outputting only 0.6v to the relay board.
I tried a different GPIO on the second ULN2803 on the pi-HAT with the exact same result.

The VCC light is on when I connect the relay board to the 5v and GND on the 10pin connector on the pi-HAT.

The ULN inputs have continuity with the GPIO outlets. The ULN outlets also have continuity with the 10pin connector.
The ULN's are also grounded on their number 9 pin and have 5v on their number 10 pin. Measuring the voltage on pin 9 and 10 gives 5v.

Can anyone help me figure out why the ULN2803 output is so low and not activating the relay?

I did the same thing. The output straight off the gpio pin is going to be 3.3 volts when on. But when you put the output through the ULN2803 the bias is reversed. The output is triggered to ground. To test with the volt meter put the ground probe on the 2803 output pin and the positive probe on the 12 volt rail. You should now see 12 volts when on. And nothing when off. Your relays will need to be set to low level trigger.

Diamond1 · Dec 4, 2018

Like I said stupid question.

So what 12v is @Ranjib talking about to use for testing.

speedstar · Dec 4, 2018

Diamond1 said:
Like I said stupid question.

So what 12v is @Ranjib talking about to use for testing.

The american DJ board power strip may use 12v relays instead of 5V

b4tn · Dec 4, 2018

You could Put the red positive test probe on the 12 volt pin of the 2803 and the ground probe on whatever output pin you are testing.

b4tn · Dec 4, 2018

speedstar said:
The american DJ board power strip may use 12v relays instead of 5V

Missed that.

buddy. · Dec 4, 2018

b4tn said:
I did the same thing. The output straight off the gpio pin is going to be 3.3 volts when on. But when you put the output through the ULN2803 the bias is reversed. The output is triggered to ground. To test with the volt meter put the ground probe on the 2803 output pin and the positive probe on the 12 volt rail. You should now see 12 volts when on. And nothing when off. Your relays will need to be set to low level trigger.

How to I set the relays to low level trigger?

b4tn · Dec 4, 2018

Do you have a link or a pic of the relays? Mine had jumpers

speedstar · Dec 4, 2018

buddy. said:
How to I set the relays to low level trigger?

Also reef-pi has an invert feature built in when setting up outlets

buddy. · Dec 4, 2018

b4tn said:
Do you have a link or a pic of the relays? Mine had jumpers

8 Channels 5V Relay Module Australia - Little Bird
https://www.littlebird.com.au/8-channels-5v-relay-module

wykat · Dec 4, 2018

buddy. said:
I posted this in my build thread but I am just going to post it here for more visibility.

I am testing out my 8 channel 5v relay boards.

First I tested with just the raspberry pi by connecting up the 5v, ground and an outlet GPIO and it worked as expected.

Next I tried with the pi-HAT but it is not activating the relay. The input of the ULN2803 is receiving 3.25v. The ULN2803 is outputting only 0.6v to the relay board.
I tried a different GPIO on the second ULN2803 on the pi-HAT with the exact same result.

The VCC light is on when I connect the relay board to the 5v and GND on the 10pin connector on the pi-HAT.

The ULN inputs have continuity with the GPIO outlets. The ULN outlets also have continuity with the 10pin connector.
The ULN's are also grounded on their number 9 pin and have 5v on their number 10 pin. Measuring the voltage on pin 9 and 10 gives 5v.

Can anyone help me figure out why the ULN2803 output is so low and not activating the relay?

Don't have your relay board, but will try to help.

Yes all components on the picture look ok (direction) and yes, no 12V is required for the relay output.

First I tested with just the raspberry pi by connecting up the 5v, ground and an outlet GPIO and it worked as expected

This is good to know. In order to replicate, can you share which GPIO port you used? What were the values of the GPIO port switching ON/OFF?

Next I tried with the pi-HAT but it is not activating the relay. The input of the ULN2803 is receiving 3.25v. The ULN2803 is outputting only 0.6v to the relay board.
I tried a different GPIO on the second ULN2803 on the pi-HAT with the exact same result.

In order for me to replicate (without relay board), can you share which pins (relay ports) you measured? Is the behavior the same with and without relay board? (Power consumption?)

The ULN inputs have continuity with the GPIO outlets. The ULN outlets also have continuity with the 10pin connector.
The ULN's are also grounded on their number 9 pin and have 5v on their number 10 pin. Measuring the voltage on pin 9 and 10 gives 5v.

If I understand correctly, wiring between GPIO/ULN/10 pin connector and power to the ULN chips are all ok. Just to be sure (don't measure voltage, measure ohm), is there a connection between pin 6 of the I2C interface on the Reef-PI_HAT and GND (pin 39 on GPIO)? This has been a failure in the initial design but should be ok on your board. [Edit]should be ok as you're measuring +5V on the ULN power pins[/Edit]