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1970s VW Diagnostic Machine

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 Tain
(@tain)
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@davee Please can I check I have understood what is going on in the circuit you drew for me?

 

https://crcit.net/c/a2efec1584954954b18032466bbc9066

 

the diodes are sized such that they reverse if voltage exceeds 3.3v, thus if the circuit is live with 12v the diode blocks.

The resistors are pulling up pins 33 and 32 unless there is a path to ground through the lamp.

 

Therefore if pin 32 or 33 read high there is an open circuit or 12v is present, if they read low there is a closed circuit

hopefully i've understood that :o)

cheers 


   
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(@davee)
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Hi @tain,

  Looks and sounds right to me ... though on recent history, my checking is clearly not as rigourous as it should be... 🙄 ... so I am not accepting any responsibility or liability.

I would add at least a pair of protective diodes, to each GPIO pin you use, as per my prevoius post, to improve the chance of your ESP32 surviving a small transient.

Good luck, Dave


   
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Inst-Tech
(@inst-tech)
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@tain Indeed, I agree with @dave that it looks and sound right..I would also suggest you breadboard the circuit example to see if all works as expected..thus saving your ESp32 from damage caused by wiring problems not seen or understood..You don't need the ESP32 for this part of the test as you can plainly see that if the there is continuity threw the bulb, the output with be ~ .7 volts ( the drop across the diode when it is forward biased), and 5 V if no continuity or 12v is present.. I too highly recommend the external clipping diodes as @Dave has suggested, schottky diodes such as In5817 should do.

good luck with your project, and please keep us informed with your progress.

regards,

LouisR

LouisR


   
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 Tain
(@tain)
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@inst-tech @davee

 

Thanks both

I've ordered schottky diodes, resistors and capacitors, plus 3 more esp32s just in case :o)

Thanks again for your help

 


   
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 Tain
(@tain)
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Hello again, hope everyone is well.

Thank you all for your help. I settled on a circuit based on the DigiKey article that @DaveE sent me.

 

I've tested with a spare rear light cluster and so far ESP32 has survived :o)  I ended up using 2 tests; the installed test wire goes to the positive side of the  lamp so I test continuity through the lamp to ground.  Then I poll each of the test wires in turn for voltage over a period of 1 minute.  Then the technician can turn on each light in succession to test the rest of the wiring, switch and any relay in the circuit. As each circuit registers a voltage it gets flagged as a PASS, at the end of a minute the rest are considered FAILED.

 

I then had to use a multiplexer as there are 8 lighting circuits in the back of the bus and so I need to use 16 pins. (8 x 2 tests)  

This all works well so I am considering this step done.

Next I am trying to come up with tests to measure 12v lead acid battery health...I didn't realize the maths is so hard for this.  I have been researching PZEM battery testers to see if I can read any data from them as a short cut. I cooked the PZEM 017 :o( I managed to read some data from it as it has an I2C eprom.  At regular intervals it sends a 1 followed by a gap then 15 numbers.  However none of the numbers make much sense.  

If any one has any other ideas I would be very grateful.

Cheers   

Tain


   
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 Tain
(@tain)
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@inst-tech Thank you, I used IN5817 as you suggested and it works a treat


   
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Inst-Tech
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Posted by: @tain

@inst-tech Thank you, I used IN5817 as you suggested and it works a treat

@tain, Great! Glad I could help you out.. VW 's are good machines..Had a Volkswagen Karmann-Ghia, and a van

back in the mid 70's.. put an alarm ckt on the Van ,  oil pressure switch, head-lite on with ignition off, using DDL (diode-diode logic) worked ok, lol

Keep up the good work..

regards,

LouisR

 

LouisR


   
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(@davee)
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Hi @tain,

   Sorry, I haven't heard of PZEM modules before, and good product reviews seemed difficult to spot.

   I did a quick Google or PZEM-017 and found

https://www.rcscomponents.kiev.ua/datasheets/pzem-017%20-datasheet.pdf

This shows an RS485 interface. Does that do anything useful?

This reference shows more about the RS 485 protocol, and entitled "PZEM-003/017 DC communication module"

https://www.solar-thailand.com/pdf/PZEM-003-Manual.pdf

-----------

Of course it might have an I2C interface as well ... but I didn't spot it beng mentioned anywhere.

Good luck, Dave


   
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 Tain
(@tain)
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@inst-tech sounds like a lifetime of experience you have there.


   
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 Tain
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@davee thanks.  Sorry It was the pzem 15 that I cooked so I moved on to the 17, I’ve ordered a serial converter to try and read the output.  However I also ordered a couple more 15s as the functionality better suits what I am trying to do.  The info on the protocol is interesting, I wonder if they use the same memory addresses in both modules.

ive been distracted by my friends garden train set.  She has asked if I can add wireless controls to them.  Been fun so far.  Used ESP32 cam , so we can get a drivers view :0).  Thinking about a train whistle next...

 

cheers


   
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