Pi driven relay

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Oddly enough, I have a system I designed that is still in production that involves soldering to #6 nuts'n'bolts.  We insist on brass, and with a gun (and traces on the PCB not much less than 1cm wide on 2oz Cu - this is a heavy-duty power board) they solder okay.  Then ring lugs with crimped wires are bolted on with yet another nut.

 

Solder tabs are supposed to do what the OP wants.  They're not that beastly to solder, even when remaining screwed on (better would be removing them, but hey).

 

S.

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jgmdesign wrote:
I have only ever had to loosen teh screw a few turns then push/pull teh wire underneath the screw head as the screw pops up when you do this. 

I wasn't driving the screwdriver, but my friend was having trouble getting the bell wire in because the solder tab kept getting in the way, and he backed the screw out far enough the nut fell off.  I dont understand why the door lock manufacturer doesn't just add the diode.  One of them sent a diode with the lock.  I guess they worry someone will connect power up backwards and have a short under power up.  On the next one I will respect Jim's experience and put the diode wire under the screw.  He knows best.

 

I think we are done with this project for the moment.  We made a video of how the door can be opened when the correct barcode is scanned and he sent it to his Guy at the post office, who is named Guy.  A green LED lights up and the relay is energized for 6 seconds if it recognizes the barcode, and a red LED if it doesn't.  Not my code and not my LEDs.  My friend, who is mainly a Qnix programmer, did that in the Pi.  He has a bug in his code that after reading 4 or 5 barcodes, the last number gets chopped off, and the red LED lights and the door wont open, and he has to restart the Pi.  Not my problem.  He said the post office would probably want a version for a real door, and I would get paid to make another relay board, probably one that plugs into the top of the Pi instead of the LCD he has on there now that uses most of the gpio pins.  He told me to figure my time and multiply by 4.  I would actually get paid!  I told him I charged $100 when I did medical device contracting and that it would take me two hours to make a board with the 4x, and he said that would be fine.  Now I am a professional.  I sort of dont want the money and all the tax documents associated with it as it is more trouble than it is worth.

 

Thanks again for all the help.  I never imagined this little project would be such a learning experience.

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 That screw is a giant heatsink.  

You are supposed to remove them before soldering.  I presume they just include them as a convenience for anyone wanting to use 'em.  That way they don't get lost somewhere.   Sorta like the spare button sewn inside my shirt 

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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But when you remove them the nuts fall into a very inconvenient spot inside the cavity, and holding them in place to get the screw started requires small fingers.  If I were on my own I would probably solder to them and worry about melting the insulation off the wires going to the coil.  I still use a 30 year old 20W Hakko soldering iron that does not have a temperature controller because I dont have much bench space for it.  I am used to the old iron and it works fine for me.  I bought 10 tips for it a bunch of years ago on eBay and shape them to chisel and fine points as needed, which works great as long as I dont file through the iron into the copper underneath.  The solder dissolves into the copper and creates voids.  I have stuck with it because of the small footprint, and I only use leaded solder.  If I need to solder to an LED emitter bonded to an eighth inch aluminum star I use a similar old Hakko 40 watt iron that gets real hot.  One of these days I will have to graduate to an adjustable iron and deal with the big controller, but I am pretty good with my little 20W iron I have been using for 10 years.  Call me old school, or cheap, but I am pretty proud of being able to fashion my own tips and get along fine with the silly thing.  If it works why change it?  One day the heater coil will fail, or i will run out of tips, and will be forced to upgrade.

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Tell your friend he will need luck to keep the Pi reliable in a real world situation. Surely there is an off he shelf solution rather than cobbling something together.

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Kartman wrote:
Surely there is an off he shelf solution rather than cobbling something together.

 

Yes and no. A modern day access control system that I use starts at around $3000.00 for two doors WITHOUT the reader or lock hardware.  A reader from an established company that has a weigand output to connect to teh Access System is several hundred dollars, plus teh lock etc....The Rpi solution is a very economical alternative.  Especially if you know how to write the code and do teh hardware interfacing.

 

 

There are cheaper access control systems out there, but Marks solution is still far more wallet friendly.

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Besides, the Post Office has officially asked for a Pi 4.  Nobody knows why they want that, but it is part of the requirements, so we are doing what was requested.

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MarkThomas wrote:

Besides, the Post Office has officially asked for a Pi 4.  Nobody knows why they want that, but it is part of the requirements, so we are doing what was requested.

The post office!?  They have been using CORBY systems for years, and are now asking for a one off access control solution?  Good for you guys

 

Jim!

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Wiegand! That’s so last century. So 125kHz rfid cards.
My point is getting the Pi reliable enough to run 24/7. Whilst the Pi is ‘cheap’, the solution may end up being so unreliable that the initial savings get evaporated in support.

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Kartman wrote:
Wiegand! That’s so last century. So 125kHz rfid cards.

While the 125khz is old and still widely used.  the Weigand interface is still the defacto standard and is on every Access System out there that I know of.

 

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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I’m more familiar with the high end stuff with encryption. Current readers are RS485 multidrop with encryption along with the cards themselves.

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Kartman wrote:
I’m more familiar with the high end stuff with encryption. Current readers are RS485 multidrop with encryption along with the cards themselves.

 

Yes, the weigand ones have that too.  Yes teh fingerprint readers have the RS485 port on them  Dealt with them at the Port Authority, bit a pain in the ass to use in that application.

 

One thing I have learned is that just when you think you have seen it all...something else comes along.

 

JIm

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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Google ODSP which seems to be the dominant protocol. Reasonably easy to implement but the challenge is securing the encryption keys.

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Kartman wrote:
ODSP which seems to be the dominant protocol.

Interesting part about its required in government applications.  No one told teh port authority of NY and NJ I guess.

 

Thanks for an update, I learned something.  Lets close this off topic as it's no bearing to teh thread. 

 

JIm

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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jgmdesign wrote:

The post office!?  They have been using CORBY systems for years, and are now asking for a one off access control solution?  Good for you guys

 

My friend has a Guy at the post office he does QNX contracts for.  Guy asked for a Pi 4 to open a door lock, and was surprised there was a circuit board involved as that was not part of the original plan.  I guess Guy thought we could just hook up the door lock to the Pi and be done with it.  My friend asked me to find a relay for 12V DC and/or 24V AC for a 250-500 mA door lock, so I did a quick look on Digi-key and chose the one with the smallest drive current thinking I could drive it with the Pi, maybe using 2 gpio pins in parallel to get the required current and later realized I should have a protection diode in there too, and we ended up here.  I still think that solution might work, inrush current aside, as the current is limited by the Pi.  But since we had to mount the relay on some sort of board, putting in the FET and doing things correctly was not that much more effort.  My friend is driving LEDs from the Pi with no current limiting resistors, and is probably getting 8 mA, which I saw on Goggle as the default gpio current, with some setting somewhere in the Pi to get 16 mA.  We never measured it as he was slammed and had other work to do and didn't care as long as the LEDs lit up for the demo video, in which I was an extra operating the door with a single line I blew at the end.  O well, so much for my acting career.

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A good source for high current relays and sockets is Automation Direct dot com. I Use a lot of their products

Jim

I would rather attempt something great and fail, than attempt nothing and succeed - Fortune Cookie

 

"The critical shortage here is not stuff, but time." - Johan Ekdahl

 

"Step N is required before you can do step N+1!" - ka7ehk

 

"If you want a career with a known path - become an undertaker. Dead people don't sue!" - Kartman

"Why is there a "Highway to Hell" and only a "Stairway to Heaven"? A prediction of the expected traffic load?"  - Lee "theusch"

 

Speak sweetly. It makes your words easier to digest when at a later date you have to eat them ;-)  - Source Unknown

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB, RSLogix user

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