Timer circuit that can ignore a persistent trigger current.

[Fleck]

If that monostable circuit doesn't work it's back to the binary counter.
Have a look at the one above. The PNP is on by the 10k resistor so when the phone brings on the NPN transistor the relay coil pulls in
One of the relays own contacts then holds the relay on. The other side of the relay contacts sends power out to the timer circuit and heater relay.
When Q14 goes high it opens Rl1 and switches everything off until the next phone call

 

[Fleck]

Looking at it again i think you can connect the 12v power out to the bottom of the 1st relay contact ie bc547 emitter, so you can use a single pole relay

 

[George]

I don't know if the 555 pin3 puts out enough power to activate the relay, if not I will use a transistor to power the coil. I'm getting the parts together now and will update shortly. If the long time delay fails with just the 555 monostable circuit I will go to your new design. Be back in a bit or maybe a byte.

 

[Fleck]

The 555 can deliver 200ma

Bc547c only 100ma



Seems the wrong way round to me

 

[George]

Looking at it again i think you can connect the 12v power out to the bottom of the 1st relay contact ie bc547 emitter, so you can use a single pole relay

Fleck I had to use a BU406 NPN because thats what I had, it is a power transistor, see datasheet attached. The circuit has turned on but it could not activate my relay so i'm just using an led to test for time. I attached the datasheet to the relay as well. Could the power transistor be consuming too much power? I am only getting 2.4v at the LED so I think something is sucking all my power. I had to use 2 1000uF caps in parallel to get near the 2200uF you had in there, my next closest was a 3300uF. Also could not find a 1.5M resistor so I just put 2 590k in series. That should not effect anything other than time so thats why I am thinking the transistor I have might be an issue. What do you think? I am still seeing if it will time out around an hour anyway because I have never tried going so long with a 555 by itself.

 

[George]

The 555 can deliver 200ma

Bc547c only 100ma



Seems the wrong way round to me

My relay has a 84mW pickup but the voltage is just too low at that point as explained above.

 

[George]

The 555 can deliver 200ma

Bc547c only 100ma



Seems the wrong way round to me

I would have thought the opposite also.

 

[Fleck]

What is the output voltage of pin 3?

Does it drop down when you connect the relay coil? If so it can't supply enough current.

The transistor sounds ok.

Just looking on the PDF It's not the 24vdc relay is it? Just thinking of all the possibilities

 

[George]

What is the output voltage of pin 3?

Does it drop down when you connect the relay coil? If so it can't supply enough current.

The transistor sounds ok.

Just looking on the PDF It's not the 24vdc relay is it? Just thinking of all the possibilities

The relay is the 5v AZ826–2C–5DME, I connected 12 direct to it just to be sure it would not burn up, I have over 4000 of these so I can spare a few. I am only getting 2.4v on pin3. I am going to take out the caps in par and res in series, change to 9vdc power supply with 220uF and 10M R for timing, this will or should give me 40 minute delay. One other thing is I did not have the .01uF cap for pin 5 and just threw in a .1uF in its place. I will take that out all together not that I think it is the problem.

It has been over an hour and my led is still on with this config so I am going to change it now.

 

[Fleck]

The output on pin 3 should be close to the supply voltage when triggered.

 

[George]

The output on pin 3 should be close to the supply voltage when triggered.

Pin 3 is fine now (7.5v on a 9v supply), that is with the coil energized. I took out the caps I had in parallel, although they = 2000uF I think the fact there were 2 had something to do with it. I am using 9v supply now with 220uF cap and 10M R for the timing sequence. This setup calculates to about 40 minutes and everything is good so far. The relay energized and I have an led set on one of the NO contacts so I will know when the relay de-energizes. I have to be at work in a few hours so I may have to continue this tomorrow morning when I get home.

 

[George]

Well it timed out around 40 min like it should but then started cycling on/off every few seconds and will not reset. Damaged the 555? Maybe, I need to sleep now so I will look into that in the morning. It looks to me like a counter will be needed for such extended time delays.

 

[Tim Metford]

Hi Guys! great job on the circuit and it's going to take me a day to work through all your posts!
I'll assemble a circuit that, hopefully, will reproduce your work using component values as close as I can get to your spec on circuit wizard.
I'd be so excited to see how this goes.

 

[George]

Hi Guys! great job on the circuit and it's going to take me a day to work through all your posts!
I'll assemble a circuit that, hopefully, will reproduce your work using component values as close as I can get to your spec on circuit wizard.
I'd be so excited to see how this goes.

That was fun yesterday but it did not work as intended for me. See what you guys can do today. I need to get some sleep as I have some 12 hour shifts the next 3 days. I'm off all next week, I will be sending your package Monday Tim. Have fun and best of luck!

 

[Tim Metford]

Hi Fleck and I trust you are well.
I've studied your posts and simulated your circuit as best I can (see below). The closest I can get to a 4020 in the Circuit Wizard simulator is the 4024 which is, I think, pretty similar to the 4020 except it's a 7-stage counter; and even then the Circuit Wizard version doesn't seem to have all the pins that its datasheet shows!

I've tried my best to combine the two diagrams you've drawn and added an extra NPN transistor to try and boost the current to the relay coil as shown, but for some reason there's not enough current to drive the coil of that DPST relay, so the circuit won't switch on (as far as circuit wizard is concerned). No doubt you'll find plenty of mistakes in what I've drawn here - please let me know!! Thanks.

 

[Fleck]

The extra transistor is just pushing more current through the base of the second, base current is usually small (collector current big) so it may have damaged the second one.
At least put a 1k resistor in the bases if you need to use 2.
How are you applying the cell phone voltage. Should be between base and ground.
If it still doesn't work measure some voltages around the transistors and across the relay.

You could also do a simple simulation to see if the transistor will switch a relay, then add the PNP underneath and see what happens

 

[Fleck]

I downloaded a simulator to try and its a nightmare to use. Which one do you use?

 

[George]

I downloaded a simulator to try and its a nightmare to use. Which one do you use?

This is a free one that is easy to use, it is the same one I have in the video clip. http://www.falstad.com/circuit/

It can be downloaded or used on the site, it is a Java Applet. When I use it it always starts with a simple circuit on it so I just hit Ctrl+A to select all then right click on the drawing and delete. To add components right click on screen to see options. To move part, select part then hold Shift and drag. To rotates or resize part hold Ctrl then click an end of the part with right mouse and drag around. Pretty simple after a few minutes of playing around.

 

[George]

Another option you might like Fleck is Cadsoft Eagle. I'm sure you know that program is for designing circuits and board layouts to send to the board house for manufacturing but it also comes with a nice LT Spice simulator. If you want to know more let me know.

 

[Fleck]

Thanks George I'll try it next time I put the computer on, which isn't that often nowadays.. Do you know of any for iPhone or android?