Delay off timer circuit

Thread Starter

merzatt

Joined Jan 15, 2009
43
I want a delay timer off circuit for my car. I want the bluetooth radio adapter to remain ON for >2 seconds when I turn off the ignition. I tapped in to the cigarette lighter circuit to power the bluetooth. It turns on when the ignition key is in position 2 (switched 12v).

I built the circuit below found from this website. http://www.bowdenshobbycircuits.info/page2.htm

delay timer diagram.gif

I also watched this video:

I used 1N4002 for diode
1000uF 16v capacitor
1kOhm resistor
NTE 102 or 2n2222 transistor
Tyco automotive relay (with a diode NTE 106)

Since I know very little about electronics, I don't know how to wire the circuit with 12V and ground where circles are shown on the diagram. What I did was to connect the battery/permanent 12V to the terminal 86 and terminal 30 of the relay. Terminal 87 to the bluetooth adapter. When I connect the battery 12V to the relay, the relay immediately kicks in even before I connect the switched 12V to the 1n4002. I don't understand why the transistor turns on the relay before I connect the switched 12V.

Can somebody tell me what am I doing wrong? Please explain how to power this circuit..
 
Last edited:

dannyf

Joined Sep 13, 2015
2,197
the R is discharging the 12v on the capacitor:

(12v/R) = C * (12v-0.7v) / t, where C is the capacitance, and t is the time.

in your case,

12v / R = 1000uf * (12v - 0.7v) / 2 sec.

Solve it for the 2 second delay you want.
 

dannyf

Joined Sep 13, 2015
2,197
My problem is, the relay turns on, even before I connect the switched 12V to the circuit.
you must be living in a universe where different laws of physics apply: it is hard to imagine this circuit acting without powers being applied.

if I were you, I would go back and think about the behaviors of the circuit you are expecting and compare that vs. the actual behaviors.

I would also double check to make sure that the circuit is correctly wired and the parts have the right pins connected.

otherwise, it is hard to help you.
 

Thread Starter

merzatt

Joined Jan 15, 2009
43
I verified the transistor pins.

Relay immediately turns on when the constant 12V is applied to terminal 86 and 30. Why the transistor closes the ground circuit even though switched 12v is not yet connected to transistors base? What I need is transistor to close the ground circuit to the terminal 85 when the switched 12V is connected to the base.
 

eetech00

Joined Jun 8, 2013
3,859
I verified the transistor pins.

Relay immediately turns on when the constant 12V is applied to terminal 86 and 30. Why the transistor closes the ground circuit even though switched 12v is not yet connected to transistors base? What I need is transistor to close the ground circuit to the terminal 85 when the switched 12V is connected to the base.
Either the circuit is wired incorrectly or the transistor is shorted.
 

dannyf

Joined Sep 13, 2015
2,197
terminal 86 and 30.
you think "terminal 86 and 30" would mean anything to anyone but you?

switched 12v is not yet connected to transistors base?
circuit wired wrong? malfunctioning devices? rail applied incorrectly? .... could be a gazillion different reasons.

to close the ground circuit to the terminal 85
what "ground circuit"? what "terminal 85"?

when the switched 12V is connected to the base.
if so, you have picked the wrong circuit to build.

You should stay back and think of this issue from your readers' perspective. they don't have the same knowledge about your circuit as you do. what you take for granted is a complete unknown to others.

So to help you help others, be concise, be specific.
 

Reloadron

Joined Jan 15, 2015
7,501
You specified an automotive relay so you want Terminal 85 going to the collector of your transistor, a 2N2222 will work fine and terminal 86 of the relay goes to an "always on" 12 volts. The Anode side of your 1N4002 goes to a switched Ignition so when ignition is On there is 12 Volts present. So on an automotive relay coil (they are standardized) #85 would be ground and in this case ground switched through the transistor and #86 is an always on 12 volt source. The Ignition 12 volts keeps the transistor turned on so the relay is energized. When the Ignition 12 volts is removed the transistor will remain On as long as the capacitor holds it on, the capacitor will begin discharging through the transistor emitter base till the base voltage drops below 0.7 volts (approximately) and then your automotive relay drops out. Also apply "always on" 12 volts to terminal #30 of your realy and whatever you are powering to terminal #87.
As drawn the circuit will work. Just a matter of getting your relay terminals correct. Both diodes can be a 1n4002 Or similar and a 2N2222 will drive an automotive standard relay just fine.

Ron
 

Reloadron

Joined Jan 15, 2015
7,501
Danny F:
terminal 86 and 30.
you think "terminal 86 and 30" would mean anything to anyone but you?

merzatt said:
switched 12v is not yet connected to transistors base?
circuit wired wrong? malfunctioning devices? rail applied incorrectly? .... could be a gazillion different reasons.

merzatt said:
to close the ground circuit to the terminal 85
what "ground circuit"? what "terminal 85"?
He did specify "Tyco automotive relay (with a diode NTE 106" Automotive relays have a standard pin out using the numbers he mentioned. There is nothing unusual about the numbers he called out. He readily admits to knowing little about electronics and just would like a little help.

Ron
 

Thread Starter

merzatt

Joined Jan 15, 2009
43
Ron, you are the man! All I had to do was to swap collector pin to Terminal 85 from 86 and it worked! I did not know the difference between 85 and 86. I was going to give up. THANK YOU!

For the future readers, 1000 uF and 2.2k Ohm causes 6 seconds of power off delay.
 
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