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Download
Harmless
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I haven't bothered to read everyone else's posts but I'm going to suggest forgetting making a "proper" interface.
Instead, get yourself a solid state relay, hook it up inside the hotplate so it can disconnect the hotplate when power is applied, and then have an
external connection which goes to a digital thermostat. On ebay and Aliexpress and those sorts of places you can pick up a thermostat that takes
K-type thermocouples for less than US$5 with shipping. The thermostat can turn the hotplate on and off for you.
Doing it the proper way might look neater, but you'll spend loads of time and money figuring it out.
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monolithic
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Quote: Originally posted by Download  | I haven't bothered to read everyone else's posts but I'm going to suggest forgetting making a "proper" interface.
Instead, get yourself a solid state relay, hook it up inside the hotplate so it can disconnect the hotplate when power is applied, and then have an
external connection which goes to a digital thermostat. On ebay and Aliexpress and those sorts of places you can pick up a thermostat that takes
K-type thermocouples for less than US$5 with shipping. The thermostat can turn the hotplate on and off for you.
Doing it the proper way might look neater, but you'll spend loads of time and money figuring it out. |
If you do this you will have to break the circuit for the heating element, otherwise you'll lose stirring as it switches the PID controlled relay on
and off.
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Twospoons
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| Quote: Originally posted by p4rtridg3 | | After testing some LM35s I got online, I can confirm that it is in fact the cold junction compensator for the probe. Now all I need to do is wire it
up. |
Its kind of surprising just how much reverse engineering can be done from a photo of a PCB.
Always makes me laugh inside when I visit a tech company and have to leave my phone at reception. When a glance inside their product will tell me
most of what I need to know...
Helicopter: "helico" -> spiral, "pter" -> with wings
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JDavis22
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Sorry to post in such an old thread. But...
Did this work? I'm about to attempt the same task.
I measured +5 on pin 5 vs pin 6 in this thread. This makes me question the other pin values.
Pin 2 seems to be ground. Pin 1 seems to be an input pulled up with a resistor.
I melted my mini din 6 plug while attempting to solder it. Waiting on a replacement now. I bought a replacement PS2 cable with leads so I can try
reversing the thermocouple if needed.
lm35 pin 1 +5v on din pin 5
lm35 pin 2 to din pin 6?
lm35 pin 3 to din pin 1 and 2
K type thermocouple + wire to pin ?3 or pin ?4
K type thermocouple - wire to pin ?4 or pin ?3
I'm using the female diagram (front view) for the pin numbers.
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Cathoderay
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I haven't been on the forum for a bit so I just saw this.
I don't think I have good news for you. I got a used Corning PC-420 a while ago. That would be an earlier version without the digital readouts.
I had to do a little bit of repair on it and in the process I did some exploration of the works. If my info is any indication the temp probes are
more complicated than at first glance, hence the high price. The PC-420 would use a Corning 400188 probe kit, I don't know if that is the same as the
PC-420D probe.
I have a more extensive amount of electronic equipment than some, including an oscilloscope. Using the standard pin numbering for a Mini Din-6
connector, you can look that up, the signals I found on the base connector are as follows.
Pin 1 a 5Hz squarewave moving between ground and +5V. (Clock?)
Pin 2 +15V.
Pin 3 +5V (possibly a resistor pulling up to +5V.)
Pin 4 No connect.
Pin 5 pulses going to ground from +5V.
Pin Ground.
Somehow the main unit must know that the external probe is connected, that may be pin 3, the probe pulls it down.
This all suggest that there is more than a temperature sensor in the probe, something translates the temperature into a pulse stream. Maybe pin 5 is
the clock and it effects pin 1. Maybe the data is put on pin 3 and its presents means that an external probe is connected.
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JDavis22
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Thanks for the reply.
Got a mini din wired up today.
I didn't pull out the oscilloscope on mine.
I'm testing below now with a small water batch at 30, 40 and 50C. So far it is holding to a +-3C from a digital thermometer placed near the probe.
1 - 2 - LM35 (3 pin transistor package, TO92-3) pin 3 (gnd)
3 -K thermocouple
4 +K thermocouple
5 LM35 pin 1 (+5v)
6 LM35 pin 2
Still testing.... (the 50C was blinking at this point)
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