# Please i need assistance with a simple timer circuit

#### Metalica

Joined Aug 1, 2010
42
Hello there,
I need help with this simple circuit which i am going to explain it for you what i am doing here.
Part 1 is a simple delay On timer circuit driving a relay.
Part 3 is a simple LED flashing circuit which flashes two LEDs so no big deal here too.
But i need some thing in between in Part 2 where the question mark (?) is to achieve the following.

1. When Main switch is closed it'll create a delay of some time before relay turns on in Part 1.

2. When relay is turned on in part 1 it'll power the circuit in Part 2 whose responsibility should be to turn on Part 3 for only 10 seconds and then turn Part 3 off as long as the main switch is not closed and circuit is receiving power.

In simple words i need part 3 to start flashing two LEDs with a delay set by part 1 when main switched is closed and Part 3 should Flash the LEDs for only 10 or more seconds before turning off completely
Now i can't find a way to do it by the use of as little components as possible and with only transistors resistors and capacitors and no 555 or any other ICs to achieve this in part 2.

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#### Picbuster

Joined Dec 2, 2013
1,027
If you know something about programming then:
LM7805
PIC12f675
1 caps 100uF
1 cap 10uF
2 resistors to be used with the leds
2 leds
1 relay
1 diode to protect relay effect
1 power switch.

Very small program

Picbuster

Joined Mar 10, 2018
4,057
Can you program, ASM, C, Basic, Sketch, Tuniot, Arduino......?

Regards, Dana.

#### Metalica

Joined Aug 1, 2010
42
@Picbuster

I want to do it using transistors only

Joined Mar 10, 2018
4,057
Curious, you want to avoid UP because of no experience in programming
or you want to do 1950's/60's legacy designs for retro fun ?

If former there is some excellent new ways of doing UP
design, like Appinventor from MIT

http://appinventor.mit.edu/explore/ For Android applications

http://easycoding.tn/tuniot/demos/code/ Uses ESP8266 module, ~ $5, for control applications Regards, Dana. Thread Starter #### Metalica Joined Aug 1, 2010 42 Curious, you want to avoid UP because of no experience in programming or you want to do 1950's/60's legacy designs for retro fun ? If former there is some excellent new ways of doing UP design, like Appinventor from MIT http://appinventor.mit.edu/explore/ For Android applications http://easycoding.tn/tuniot/demos/code/ Uses ESP8266 module, ~$5, for control applications

Regards, Dana.
I want to do it using transistors and RC components only because i feel comfortable with analog electronics

#### crutschow

Joined Mar 14, 2008
28,196
A 555 is mostly analog.

#### Alec_t

Joined Sep 17, 2013
12,311
If you don't want to use any ICs, try this :

R2/C2 set the 'on' delay. R1/C1 set the 'off' delay. M2 switches the negative rail 'ee' of the multivibrator. D3 and D4 prevent breakdown of the base-emitter junctions of Q1 and Q2 when reverse biased.

#### Metalica

Joined Aug 1, 2010
42
If you don't want to use any ICs, try this :
View attachment 163386
R2/C2 set the 'on' delay. R1/C1 set the 'off' delay. M2 switches the negative rail 'ee' of the multivibrator. D3 and D4 prevent breakdown of the base-emitter junctions of Q1 and Q2 when reverse biased.
Wow i am so happy with this, thank you thank you so much for this.
You have given me a very nice idea i never thought of that and so flaw less.
Can i use NPN transistors instead of NMOS.
Please do tell me what software you used to simulate this i use EWB old version 5.12.
And please tell me more about D3 and D4 what you mean by break down is it break down voltage or physical break down of Q1 and Q2.
Thank you.

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#### Metalica

Joined Aug 1, 2010
42
If you don't want to use any ICs, try this :
View attachment 163386
R2/C2 set the 'on' delay. R1/C1 set the 'off' delay. M2 switches the negative rail 'ee' of the multivibrator. D3 and D4 prevent breakdown of the base-emitter junctions of Q1 and Q2 when reverse biased.
Please sir tell me which NMOS transistors can i use and the transistors should be easily available.
Thank you

#### Alec_t

Joined Sep 17, 2013
12,311
Can i use NPN transistors instead of NMOS.
Using NPN transistors would require significant base current, hence timing components would need to have much higher values or Darlington connections would be needed. I'd suggest 2N7000 as a suitaple MOSFET.
Please do tell me what software you used to simulate this
what you mean by break down
If the base-emitter junction of an NPN transistor is reverse biased by more than about 5V the junction can be damaged due to an avalanche effect. D3 and D4 connected as shown clamp the reverse voltage to about -0.7V. They could each instead be positioned in series with the respective transistor base.
Incidentally, if you intend this circuit for automotive use (which the 12V supply hints at) it will require 'beefing up' to protect it from transient and reverse polarity pulses.

#### Metalica

Joined Aug 1, 2010
42
Great i have learned so much today . thank you very much