Hi,

I have the parts and tried to get it working on the breadboard with a relay but it does not work. Can you look at the picture and see if I have it correct.

 

hi Nick,
Check the pins of the two semiconductors.
I have marked the pins Idents.
E

 

I have the pinout OK. Just trying to get it to work on the breadboard without connection to the actual unit. I have a relay on the breadboard. Just want to get the delay working but it just won't.

 

I have the pinout OK.

Look again at Eric's pin designations.
You appear to have the source and gate of Q1, and the emitter and collector of Q2, interchanged.

Edit: I also don't see diode D2 from my schematic.

 

sorry guys I have tried everything with this and just can not get it to work. I guess I will have to try and figure something else out on this one.

 

hi Nick,
This image shows how the Bread board circuit is configured.
It should work as Carl as states, when you say is does not work, what exactly do you see or not see, that indicates it is not working.?

We need a more detailed fault report, measure the voltages on the transistor/FET pins withthe INPUT disconnected and also with the INPUT connected to +12v.

Post the values.

E

 

guys, thankyou for your patience with me, I have started again and rebuilt the circuit with new components and jumper wires and it seems to be working now. I have more tests to do but would seem something was faulty somewhere. I will test it properly and let you know. Thanks again. It's great because it is only minimal space required.

 

Glad you got it to work.

 

You are a star and I can not thank you enough for putting up with my complete lack of knowledge. Same goes for you too Eric. I could not have got this far without both your help.

 

Hi guys. Having spent some time with the delay circuit and replaced the 200K with a 500K POT. it would seem that the higher the resistance level, the more fluffy the relay de-energise gets. Is there a way round this. 555 timer is a no go because as the high low input is toggled, the delay should reset. What I mean by that is that if the probe is right on the water level and the circuit is switching on and off quickly, the delay countdown should restart. The 555 timer circuit does not reset. Carls circuit does this well but I need the relay action to be solid. Any ideas.

 

Hi guys. Having spent some time with the delay circuit and replaced the 200K with a 500K POT. it would seem that the higher the resistance level, the more fluffy the relay de-energise gets. Is there a way round this. 555 timer is a no go because as the high low input is toggled, the delay should reset. What I mean by that is that if the probe is right on the water level and the circuit is switching on and off quickly, the delay countdown should restart. The 555 timer circuit does not reset. Carls circuit does this well but I need the relay action to be solid. Any ideas.

What do you mean by "solid"?
A relay is either on or off so I don't understand the problem.

 

What do you mean by "solid"?
A relay is either on or off so I don't understand the problem.

Relays should click when they energise or de-energise, the cap feeds the p channel mosfet, obviously the voltage degrades slowly, this means the mosfet only conducts partially and the relay does a very quiet almost double click. The greater the resistance the less positive the relay action.

So by saying solid, I mean a proper relay click rather than the half hearted action at higher voltage.

 

Here's the circuit modified with a simple fix to improve the relay switching time and remove the "fluff" (wish all problems were that easy to fix).
I moved the timing capacitor connection from +12V to the relay transistor to provide some positive feedback to the MOSFET gate, which should provide a snap-action when the relay turns off after the delay.
Note how the V(g) MOSFET gate voltage snaps to 12V, fully turning off the MOSFET, when the relay de-energizes after the delay time.

 

Here's the circuit modified with a simple fix to improve the relay switching time and remove the "fluff" (wish all problems were that easy to fix).
I moved the timing capacitor connection from +12V to the relay transistor to provide some positive feedback to the MOSFET gate, which should provide a snap-action when the relay turns off after the delay.
Note how the V(g) MOSFET gate voltage snaps to 12V, fully turning off the MOSFET, when the relay de-energizes after the delay time.

View attachment 118893

Thanks for the input yet again......

I have tried this and because the way the delay circuit is connected to the rest of the circuit it pops Q1. I now have all the logic on a darlington array, this controls the normal relay state via a jumper, the steam, water and fault leds. I have used the last slot on the darlington as Q1 and it seems to be more positive on the relay de-energise, not as positive as I would like but still better than before.

The total part count now for the delay circuit, 3 leds, relay and the switching logic is 15.

 

Hi

Maybe this will work. Instead of a slow current decay, the comparator output provides a switched input to the mosfet driver Q2. I used an arbitrary mosfet so you would need to choose properly sized one.