Power Controller Build Needs Help Please :-)

[Fish Fan]

Hi guys! I am in the process of trying to cobble together a Reef-Pi controller, and I could use some help, please. I have posted in the main thread, but I feel bad adding to an already bloated read, so I'm hoping some of you will be willing to help me here.

Consider me a noob with this stuff. I do have a background in tech, but I am super rusty

Here's where I am in short:

I completed the Reef-Pi install, and am now working on my power controller build. I would prefer not to use the American DJ power strip recommended in the Reef-Pi documentation for a number of reasons. I would prefer to go with a DIY bank of regular household duplex outlets. I've done this before with other RPi projects and I am aware of and alright with the safety concerns with doing it this way.

I have soldered up my Adafruit Perma Proto HAT as per the Reef-Pi guide, and I have a 12v 8 channel relay board I'm trying to control. I'm just in my initial testing phase here. My problem is that I can create outlets in Reef-Pi 6.0, I can turn turn those outlets on and off, and I get an expected 3.3v on and off coming out of the RPi GPIO and flowing right into the legs of my ULN2803A Darlington. The problem is that I cannot get any output from the ULN2803A. I have 12v coming into pin 10 (com) of the ULN2803A. Everything on my Perma Proto Board seems to check out with visual inspection (no solder bridges) and a continuity tester. I can't figure out why everything works basically right up to the ULN2803A, and then there is no output afterwards.

An obvious thought is that my ULN2803A chip is defective, and I've ordered more that are supposed to be here tomorrow. I'm not convinced that my ULN2803A chip is faulty, but at least I can rule it out.

Could someone please help me figure out why I have expected voltage coming into the ULN2803A chip, but I get nothing on the output side?

I would very much appreciate any help here, thank you in advance for your help!

 

[Sral]

Hi, as I have eluded to in the main thread, the ULN2803 is a transistor IC, that acts very similar to a relay with the addition that it also has directionality.

You need to wire it similarly to how I have done it with the ULN2801 ICs that I have used in my doser module, just without the additional limiting input resistors and the PWM inputs:

You will only measure a voltage change on the output when a load is connected to it. When it#s off, out is at VCC, or 12V in your case, when it’s on voltage will drop to somewhere between 0-1V depending on the circuit and the load current.

In your case you’d need to supply your relay board with 12V and connect the relay board‘s IN channels directly with the ULN2803‘s OUT channels.

 

[Fish Fan]

Hi, as I have eluded to in the main thread, the ULN2803 is a transistor IC, that acts very similar to a relay with the addition that it also has directionality.

You need to wire it similarly to how I have done it with the ULN2801 ICs that I have used in my doser module, just without the additional limiting input resistors and the PWM inputs:

You will only measure a voltage change on the output when a load is connected to it. When it#s off, out is at VCC, or 12V in your case, when it’s on voltage will drop to somewhere between 0-1V depending on the circuit and the load current.

In your case you’d need to supply your relay board with 12V and connect the relay board‘s IN channels directly with the ULN2803‘s OUT channels.

Thank you for your help! I have my ULN2803A wired exactly like your diagram. I'm doing it exactly as described in the Reef-Pi power controller guide. I have pin 10 connected to 12v, I have pin 9 connected to ground. I have, for example, pin 1 connected to the RPi's GPIO and corresponding pin 18 connected to my relay. Nothing is happening on the output side of the ULN2803A. I've checked and double checked with a continuity meter and all my connections and solder joints on the Proto HAT seem fine, including the grounds. I have more ULN2803A chips on order, they should arrive later today. Maybe, just maybe, I have a bad chip. Is there any other reason my circuit isn't working?

Thanks again for your help!

 

[Sral]

Thank you for your help! I have my ULN2803A wired exactly like your diagram. I'm doing it exactly as described in the Reef-Pi power controller guide. I have pin 10 connected to 12v, I have pin 9 connected to ground. I have, for example, pin 1 connected to the RPi's GPIO and corresponding pin 18 connected to my relay. Nothing is happening on the output side of the ULN2803A. I've checked and double checked with a continuity meter and all my connections and solder joints on the Proto HAT seem fine, including the grounds. I have more ULN2803A chips on order, they should arrive later today. Maybe, just maybe, I have a bad chip. Is there any other reason my circuit isn't working?

Thanks again for your help!

Sounds good so far. Can you make a photo of the circuit and the load connections as well as the relay board ?

If you have no voltage on the output side it would mean that your load isn’t connected properly.

 

[Fish Fan]

Sounds good so far. Can you make a photo of the circuit and the load connections as well as the relay board ?

If you have no voltage on the output side it would mean that your load isn’t connected properly.

I can, but I may be going in another direction. When I started this build I wanted to deviate as little as possible from the Reef-Pi documents. To that end, I got a 12v relay board and have ever since been trying to get this darn circuit working. But, I had on hand a couple of 5v relay boards that I've used on other projects where I powered and controlled the relay boards directly from the the RPi. So with that in mind, I removed the Proto HAT with the ULN2803A circuit and I have the RPi running "HAT-less" with Reef-Pi installed. Then, just with using jumper wires I connected ground on the relay board to a RPi GPIO ground pin and the VCC on the relay board to a 5v pin on the RPi. Then I connected In1 on the relay board to GPIO pin 34 and like magic it just works! I can push the Equipment 1 on/off button in Reef-Pi and feel a certain sense of self satisfaction every time I hear the relay click lol!

But seriously, I think this solves my problem. I can get rid of 12v and the ULN2803A circuit altogether and just drive the relay board from the RPi. Or, it would be no problem to supply 5v directly to the relay board, if that's better.

Do you see a problem with doing it like this?

Thank you for your help!

 

[Fish Fan]

Hey again, maybe someone can help me, but I've been beating my head against the wall for several days now, so I'm at a loss.

I have my power controller relay board working as described in one of my most recent posts, using the Raspberry Pi to supply power and ground to the relay board, as well as the control signals. No other circuitry.

That said, I took another shot at recreating the 12v, ULN2803A circuit I was messing with before (and as described in the Reef-Pi Power Controller documentation). I thought maybe I got over confident in my solder skills (though I can't find any flaws in my soldering on the Perma Proto Board (both by visual inspection (magnified with my phone) and with the continuity meter).

I bit the bullet and pulled out my breadboard kit, and attempted to recreate the ULN2803A circuit using a breadboard. I have everything connected as @Sral described in post #2 of this thread. Once again, I am getting 3.3v from the Raspberry Pi flowing into the ULN2803A, but nothing on the output side of the ULN2803A.

At this point I think I can proceeded in my Reef-Pi build by connecting the relay board directly to the Raspberry Pi, but it's driving me crazy that I can't recreate the "official" Reef-Pi power controller circuit.

Does anyone have any idea what I'm missing here? It's driving me nuts, or at least nuts-er ;-)

Any help would be very much appreciated!

 

[Sral]

Hey again, maybe someone can help me, but I've been beating my head against the wall for several days now, so I'm at a loss.

I have my power controller relay board working as described in one of my most recent posts, using the Raspberry Pi to supply power and ground to the relay board, as well as the control signals. No other circuitry.

That said, I took another shot at recreating the 12v, ULN2803A circuit I was messing with before (and as described in the Reef-Pi Power Controller documentation). I thought maybe I got over confident in my solder skills (though I can't find any flaws in my soldering on the Perma Proto Board (both by visual inspection (magnified with my phone) and with the continuity meter).

I bit the bullet and pulled out my breadboard kit, and attempted to recreate the ULN2803A circuit using a breadboard. I have everything connected as @Sral described in post #2 of this thread. Once again, I am getting 3.3v from the Raspberry Pi flowing into the ULN2803A, but nothing on the output side of the ULN2803A.

At this point I think I can proceeded in my Reef-Pi build by connecting the relay board directly to the Raspberry Pi, but it's driving me crazy that I can't recreate the "official" Reef-Pi power controller circuit.

Does anyone have any idea what I'm missing here? It's driving me nuts, or at least nuts-er ;-)

Any help would be very much appreciated!

Can you provide a picture of the circuit ? That’s typically the first place to start ^^

 

[Fish Fan]

Can you provide a picture of the circuit ? That’s typically the first place to start ^^

Yes, I will try to get a picture of this tomorrow. I appreciate your help, and cannot figure out what I'm doing wrong, so I would appreciate any help I can get.

Thank you again for your help!