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Very basic and simple help required for circuit to mod a coffee machine

MrShades

Mar 26, 2016
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Mar 26, 2016
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I'm working on a simple project with off-the-shelf modules, that will add volumteric control to a home espresso machine (what this essentially does is use a hall-effect flow meter on the tank-to-pump pipe coupled with an electronic timer relay (in counter mode) that counts the pulses from the flow meter, stopping the coffee machine at a preset count). Simple...

However, whilst this all starts very nicely when the 'brew' switch is hit - and the machine stops automatically at the preset point - the electronic timer relay then needs to be manually reset (by hitting a "reset" button on it). I'd like to avoid this if possible, but I can't think of an easy way to do it.

What needs to happen is:

1. There's a 240V circuit that drives the pump, that's switched on when the brew switch is on - I'd like to use this as the initial trigger. There's then a pin on the timer controller that, when connected to +12V (another pin) momentarily will reset the counter (as if 'pushing' and releasing a momentary push "reset" switch)

2. So, when this 240V circuit is switched on, I'd like a separate 12V circuit to go on briefly and the off again - and remain off (until the 240V is switch off, reseting the circuit).

With my very basic knowledge, I'm assuming that there's going to be a 240V relay that, when energized, will switch the 12V circuit - but I only want that 12V circuit to remain on very briefly (perhaps 0.1s) and then switch off again.

Can anyone help me with a relatively simple way to do this, and avoid having to manually press this "reset" button all the time?

Many thanks for any help or advice that anyone can offer.
 

Arouse1973

Adam
Dec 18, 2013
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5,178
Hello and welcome to EP. This is quite straight forward but we need to know how much space you have to fit the electronics.
Thanks
Adam
 

MrShades

Mar 26, 2016
4
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Mar 26, 2016
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Thanks for the reply and thanks for the welcome Adam.

Space isn't at a premium, as I have quite a bit of space inside the coffee machine and also some within the external box that I'm housing the 1/16DIN timer relay in.... cost is more of an issue, as I'm trying to sort this on a budget (otherwise I'll just stay with pushing the Reset button between shots!)
 

Arouse1973

Adam
Dec 18, 2013
5,178
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Ok so options are, buy a ready made mono-stable module and use a wall wart power supply. Or build something yourself...your choice
Adam
 

MrShades

Mar 26, 2016
4
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Mar 26, 2016
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Thanks for that. Actually, I'd already looked at using an off-the-shelf 555 timer module, but thought that there must be some way of doing it in a simpler or more elegant way with a relay and some sort of RC circuit using discrete components. I've got a 9V DC power feed available, from the TDR/counter, but the 555 modules seem to demand 12V (and many comments show that they don't work below 12V) - so I'd prefer to find some way that will work either on the 9V side (and turn the RST line off again, after a brief 'on' period) or on the 240V side (and do the same to a relay or SSR).
 

MrShades

Mar 26, 2016
4
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Mar 26, 2016
Messages
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Digging around a bit further, it looks like a 555 is about the only way to build a non-retriggerable monostable multivibrator.... but I'll keep looking.

Thanks for the advice.
 

Arouse1973

Adam
Dec 18, 2013
5,178
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5,178
Digging around a bit further, it looks like a 555 is about the only way to build a non-retriggerable monostable multivibrator.... but I'll keep looking.

Thanks for the advice.
No no no....other ways to do it.
 
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