Advice on hardware hacking project - Smart Door Opener - Voltage Regulator

Hello all!

Back story

I'm working on "hacking" a Skylink DM-50 Swing Door Opener. I bought it used on eBay for parts (was missing some things including the wireless remote to control the device but the motor was operational). Device User Manual. Going to integrate this device into my smart home for automation :smiley:

I bought this Arduino based dev board to replace the missing wireless remote: NodeMCU ESP8266 ESP-12e (Product Flyer)

So far, with the help of reading through other people's projects on this forum, I was able to get this dev board to simulate a button press to open/close the door (to replace the missing wireless remote). This Skylink device has an option to connect an external button to activate the door. The terminal connection on the circuit board (T3) for this has two pins; 1 pin outputs +3.92v and the other pin is the ground 0v. If you bring the +3.92v down to ground, it will activate the motor/door.

Photos of my project

I used a NPN transistor (2n2222a), connected the collector to the +3.92v pin, the emitter to the 0v pin and the base to a 1k resistor which then connected to my dev boards digital pin. I also have my dev board grounded to the same ground as the Skylink circuit board. Now when I bring the digital pin HIGH for 1 sec, it simulates the button being pressed and activate the motor :slight_smile:

This is where I need help

My next goal is to power this dev board by stealing power from the Skylink's board (so I don't have to supply power VIA external USB cable). My dev board runs off +3.3v but also has a Vin pin that connects to an on-board voltage regulator. This regulator can take +5v min and up to +10v max and supply a constant +3.3v.

I've already tried to connect the +3.92v to Vin but it wasn't enough to power the board. I'm afraid to connect the +3.92v to the dev boards +3.3v in fear of burning something up. Is this a valid fear?

I checked multiple points on the Skylink board but could not locate a +3.3v source. I found a terminal on the Skylink board (T2) which is suppose to be used for enabling/disabling external power source for the electromagnetic lock. The positive pin on this terminal is usually around +31v to +32v max when motor is not in operation. When I activate the motor, this voltage varies. The lowest I see it drop is about +26.5v. It varies while the motor is running (about 6 to 8 seconds) then returns to about +31v to +32v max.

I'm thinking I can use this fixed voltage regulator ua78m (datasheet) to supply it the +26v to +32v input and get +5v out in which I can use to connect to the Vin of the dev board. But looking at the datasheet and the recommended operating conditions, it seems the voltage I would use is a little too high (they show +30v max)? Would this regulator work for my needs? Do I need a different regulator? Perhaps a 10v regulator instead of 5v? Is it okay to regulate a power source twice (+32v down to +5v; then the dev board's on-board regulator going from +5v to +3.3v)? Lastly, once I have the correct regulator selected, how would I wire this up? Would I use capacitors in any fashion?

From what I've been able to research, a regulator is what I need but don't know the specifics. While not necessary, it's recommend to use capacitors as the regulators datasheet specifies. And since I see the voltage line I want to use fluctuate, I think I'll need to use capacitors, correct?

I appreciate any help at all in helping a noob get my first "hacking" project completed :slight_smile:

I would tend to say that if the switch pin on your door opener board has a 5 V logic voltage on it (which is what the +3.92 V is) then some part of it will be powered by 5 V.

If you post some high resolution pictures of the board - preferably both sides - in good light, we could possibly direct you as to where to look. :grinning:

You will probably be OK to use 3.9V on the 3.3V pin of the Arduino. But if the only source of 3.9V is the button pin, it will not be able to provide enough current.

You are right to be cautious with the almost 30V. With a motor there could be damaging spikes on that line.

Search the Pololu website for a power supply that will handle 45V surges. You may have to do it in 2 stages, like 30V to 12V to 3.3V. At that point it is cheaper and maybe more convenient to use a wall-wart plugpack.

Paul__B:
If you post some high resolution pictures of the board - preferably both sides - in good light, we could possibly direct you as to where to look. :grinning:

I uploaded some more pictures; hopefully better lighting and closer details :slight_smile: Skylink Door Opener - Integrated into Samsung SmartThings Hub - Album on Imgur

If need be, I can remove the motor to get pictures of the components behind the motor. Let me know and I can get that done.

If we can find this +5V line, that would be my MOST ideal setup :smiley:

MorganS:
Search the Pololu website for a power supply that will handle 45V surges. You may have to do it in 2 stages, like 30V to 12V to 3.3V. At that point it is cheaper and maybe more convenient to use a wall-wart plugpack.

Doing some more research, if I were to regulate +32V to +5V, I'd be putting off some heat and would likely need a heat sink on the regulator. Running two regulators in series as you mentioned is another thought I have and is still a possibility :). The other possibility is running a long USB cable to power up the dev board but what's the fun in that ;). It'd be much cooler to have it all integrated with one power source.

Thank you guys for your time!!!

Forum members don't like clicking on links to external image hosting sites, so please attach your images to your post on this forum. Once the attachments are posted, you can copy the address of the attachment, and then modify the post and embed the image using the "insert image" icon.

Another possibility for powering your board would be to use a dc-dc convertor. These are more efficient and generate less heat.

Ah! I missed the photo link in the Original Post.

xtreme22886:
If need be, I can remove the motor to get pictures of the components behind the motor. Let me know and I can get that done.

Obviously. :grinning:

Also explain what each of those wires are.

Paul__B:
Ah! I missed the photo link in the Original Post.

Obviously. :grinning:

I have no clue what I was thinking :o ! Of course you'd need to see that lol

I wish I could upload the images to this post but with a limit of 2MB, it's hard to get a "hi-res" photo posted. I've updated the imgur link with new pictures of the front/back of the board removed from the motor chassis.

Paul__B:
Also explain what each of those wires are.

The white cable strung across the top of the board is the wireless antenna for the wireless remote for the unit.

The yellow, 2x green and 2x white connect the circuit board to the motor. (hope that answered your question)

PaulRB:
Another possibility for powering your board would be to use a dc-dc convertor. These are more efficient and generate less heat.

Reading up on these now! Thank you!

Did some more poking around on the board. Found several +14V locations. I'm going to get a +5V fixed voltage regulator and run it off the +14V line :slight_smile: . Thanks for all the suggestions and offers to assist!

Right! The image I wanted.


OK, so what is that TO-220 component with the tab sticking up in the top right part of the board just to the left of the relay?

Paul__B:
OK, so what is that TO-220 component with the tab sticking up in the top right part of the board just to the left of the relay?

That is a BT139-600E; planar passivated sensitive gate four quadrant triac (datasheet)

Datasheet says it's applications are general purpose motor control and switching.

Not a regulator then.

Well, I am surprised that it does not have some part running at 5 V, particularly if you determined a 5 V logic voltage on the switch input.

Paul__B:
Not a regulator then.

Well, I am surprised that it does not have some part running at 5 V, particularly if you determined a 5 V logic voltage on the switch input.

I did a lot of continuity testing last night. I traced those +3.9V pins all the way back to the green 48R30 IC chip (datasheet). That chips operating voltage is between 2.4V-5.2V. Pin 20 is the VIN and it's also +3.9V. I found the VIA point on the circuit board that is powering this IC and it's +3.9V. It's also powering nearby LED and buzzer. I failed to located the beginning source of this +3.9V line though.

I did something that I thought was cool. I used my light on my phone to shine up underneath the board which allowed me to easily see the traces in the circuit. Based off trace thickness I was able to locate other +3.9V sections. Based off thickness I found the +14V line which is also hitting several components. Ground traces tended to be the largest connecting multiple ground at the same time.

I'm going to my local electronics store on Saturday to pick up a NTE1910 9V 1A voltage regulator (datasheet) and I'll connect that to the +14V line I found. Should be good. Don't plan on wiring up a cap or anything because I'm going to feed this +9V to my dev board's VIN which has an on-board regulator (min +5V; max +10v) and such.

I'll let you know it goes over the weekend.

It's better to go straight to 5V with a switchmode DC-DC converter.

After your success with this 9V part, keep in mind that in general, 3-terminal regulators will not function without a minimum capacitance connected.

I thought you said you were using a NodeMCU? What makes you think 9 V is an appropriate supply voltage for it? :astonished: 5 V maybe.

Paul__B:
I thought you said you were using a NodeMCU? What makes you think 9 V is an appropriate supply voltage for it? :astonished: 5 V maybe.

I am yes. I was thinking 9V over 5V because it is being sold cheaper at my local electronics store, on the back of the NodeMCU it's printed min 5V; max 10V for VIN, 9V is in-between the board min/max VIN and others use a 9V battery to power these guys up so I figured since the 9V regulator was cheaper than the 5V, it would simply act as a 9V battery and all would be good.

It's only a few dollars difference but would it be a big difference to use the 5V instead?

The price difference between a 9V regulator and the 5V version, from the same component family, should be zero. The manufacturers' production cost is the same, and they sell them for the same price, as long as you buy in the same quantities.

So I would ask your local store why the two models are different prices (assuming they are the same manufacturer and product family) and ask if they will sell the 5V to you at the same price as the 9V.

PaulRB:
So I would ask your local store why the two models are different prices (assuming they are the same manufacturer and product family) and ask if they will sell the 5V to you at the same price as the 9V.

Thank you for your input. I'll be going to the store tomorrow and will get a 5V regulator and look at dc to dc converters :slight_smile:

Update:

Went to the local store. Ended up getting a DC to DC convertor :). Everything is all good now; just need to mount it on the door to complete the setup.

Thanks for everyone's input on my project! Much appreciated!