Timer circuit that can ignore a persistent trigger current.

Tim Metford

Tim Metford

New Member
#21
#21
I can see the pin layout on the datasheet which is a good start! However, with regard to the reset pin and Fleck's comment earlier where he said:-
"I couldn't remember what to do with the reset pin ie leave it high or low. It'll all be on the data sheet for the IC anyway"
I've studied the datasheet (thanks George) which says "a high level on the RESET line resets the counter to its all zeros state" I don't understand enough to work out from that how to connect the reset pin (11) though I've given it a go in my diagram below.
Added to this, the version of Circuit Wizard that I've got doesn't permit its 4020 chip to function (it kindly asks me to upgrade if I want this facility), however, I'm not ready to upgrade this software just yet so I need your help to complete a circuit diagram that you think should work and I'll give it a go.
Below is my attempt at adapting Flecks' diagram by adding in the ceramic capacitors you suggested. The pins labelled in red represent the pins I would connect to on the real chip because the version on Circuit Wizard doesn't possess all the pins.
Flecks circuit in CWZ.png

Would you kindly check this over to see if I'm in the right ball park here please?
BTW, all comments received with gratitude! :)
 
F

Fleck

Member
#23
#23
Yes I remember now about the function of the reset pin... Hmmm thing is if it's just left to run it'll come on for an hour and go off for an hour. Then come on for an hour.. Etc etc

Err.. Thinking time....
 
George

George

Moderator
#24
#24
Fleck said:
Yes I remember now about the function of the reset pin... Hmmm thing is if it's just left to run it'll come on for an hour and go off for an hour. Then come on for an hour.. Etc etc

Err.. Thinking time....
Click to expand...
Fleck,

Please correct me if I am wrong here. I was thinking if the pin 11 was connected to ground through a resistor instead of cap wouldn't that allow the counter to reset to a normal state after the timing process has completed? Just a thought and could be way off on this one.

I have literally thousands of IC chips but not one single one of these, damn!

George
 
F

Fleck

Member
#25
#25
I've got in the back of my mind that there's a pin that enables the count or something, so it could be used to stop the counter at 11111111111111 and then you could use another monostable on the output (via capacitor) to time one hour light.
I'm struggling for internet at the minute otherwise I'd look myself.

Also have you considered using high powered LEDs? Seems awfully 1980's using a relay.
 
F

Fleck

Member
#26
#26
Yes George it does reset to 0000000000000 after 11111111111111 anyway.
The reset pin will reset any number to 00000000000000 and the counter will just continue counting up from there again
 
George

George

Moderator
#29
#29
Well I have 4400pcs BC557A (45v) 1400pcs BC557B (65v) in stock if you need them Tim, I would be happy to mail a couple for free to help you out as well as the resistors and cap if you need them. The caps are ceramic SMD and the resistors I have TH, SMD, and Resistor network Arrays. I don't mind helping out people on this board so just let me know.
 
Tim Metford

Tim Metford

New Member
#31
#31
George, thank you for your kind offer of those components! Most generous of you. I'll see what I can source from Maplin first, (Maplin's easy for me because it's close to where I work). Having said that, Maplin's got the BC556 and BC558, but not the 557!
Will either the 556 or 558 will do the job? I'll see what I can get from Maplin's first, and get back to you if there's a problem.

Hi Fleck, thanks for your revised circuit diagram but I'm not sure what the chip is that you've drawn there. I searched for, but couldn't find the CMOS Logic 2014, so would you clarify what the chip is please and I'll see if I can get it.
Fleck said:
This is more like it lol

Click to expand...
Thanks guys, really appreciate your support!
 
Tim Metford

Tim Metford

New Member
#34
#34
Fleck said:
It's the same 4020 counter Tim
Click to expand...
Hi Fleck, I’ve been trying to work out how your diagram is supposed to work – I’m sure it’s my lack of electronics knowledge that's the problem so I’d really appreciate your help here!
Puzzles
1. Your diagram shows both PNP transistors connected together via their bases (with a 1k resistor in between). How is the current supposed to flow in order for the transistors to operate correctly?
2. What electrical signal occurring in the 4020 will cause the switching off of the relay coil, and what path would this signal take to do this? I cannot see any direct connection between output on the 4020 and the relay coil (unless it is my lack of knowledge about the behaviour of the PNP transistors which is highly likely!)
Thanks for your help.
 
Tim Metford

Tim Metford

New Member
#35
#35
Ah! Following on from what I've just said I've re-read Fleck's earlier comment: - "When output 14 goes high it switches off both transistors, which disconnects the clock pulses and switches off the relay coil"
So that might answer my own question even though I don't understand the properties of the PNP transistors well enough to understand what actually goes on here.
 
F

Fleck

Member
#36
#36
Put another 1k resistor on the base of the right hand transistor, I missed that off.
PNP transistors are opposite to NPN transistors as in that they switch OFF when a positive voltage is applied to their base.

I usually use NPN if I can
 
Tim Metford

Tim Metford

New Member
#37
#37
Fleck said:
Put another 1k resistor on the base of the right hand transistor, I missed that off.
PNP transistors are opposite to NPN transistors as in that they switch OFF when a positive voltage is applied to their base.
I usually use NPN if I can
Click to expand...
Thanks Fleck, does that mean there'll be a total of 2K ohms between the two PNP transistors, with the connection with Q14 coming between the two 1k resisitors?
 
F

Fleck

Member
#40
#40
with regards to how transistors work, I will attempt to explain with the aid of a sketch comparing a transistor to a relay:



a voltage on the b input on the top diagram would close the relay and light the lamp.

a voltage on the base of the NPN transistor would also light the lamp as it would conduct through the collector (c) down to the emitter (e)

transistors are much better than relays though.. they are not simply on or off like a relay, they are semi-conductors as well, they can be used to amplify waveforms ie music, radiowaves etc which are everything in between.
 
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