Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

electric ignition timer circuit, need help w/

Status
Not open for further replies.

bd13

New Member
I want to make a timer that will ignite an eletric igniter (chemical based) when timer reaches 0 (what else would it do?) I already have the timer, thanks to the dollar store, it is a simple kitchen timer that beeps when the time is up. I know that i can hook up a latching circuit to the speaker terminals to get a steady voltage when the thing starts to beep, and then i make the latching circuit trigger a relay which completes a simple circuit that ignites the igniter. but there is one problem: its too big, i need this whole idea smaller and use less batteries. I need some way for a 9v battery to operate the latching cicuit and also ignite the igniter, or a small 1.5v button battery operate the latching at the 9v just ignite the igniter. and i can't just hook the igniter to the output of the latching circuit because the transistors take too many volts away from the 9v so in the end it can't ignite anything, but alone it can ignite the igniter. i only have a small area to fit this and 80% is taken by the timer and the 9v, i know i can fit a 2 transistor latching circuit in the leftover space but i need to somehow make a circuit between the igniter and the 9v with as little resistance as posible (very little). anyone have any ideas? thanks
 
Explain more. What are you doing exactly.
Is this for a Model Rocket?
A Glow plug on a Model Airplane?
Do you want a circuit that will ignight from the audio sound of the beeper?
How much Space?
Do you already have the Igniter Circuit?
If so where is the schematic for it so a circuit can be designed for it?
More Details.
 
ok, here is the latching schematic i'm using (from Exo):


-this is for model rocketry, so the igniter is a peice of nichrome with some bp on the end (made 'em myself so there is a lot of bp on the end)
-the idea behind this is that i want the thing to ignite when the timer starts to beep, and because it beeps (high low high low) i need a latching circuit to change that into a steady high current which can ignite the igniter. but because i can only have one 9v i need the 9v to power the latching circuit and ignite the igniter. but the transistors take too much away from the current so it can't ignite the igniter just by hooking the igniter where the res. and led are (res. and led are taken out). and the 9v does, alone, have enough current to ignite the igniter.
-i'm tring to fit this all into a altoids container, which is say 4 by 2 inches. the timer and 9v leave only about a 1/2" by 2" for this circuit. i think i can fit it in that area but i need it to work first. (please don't just give up because of the small size, let me be the judge of size and how it will fit in, i can always change things)

the latching circuit is triggered by a the pluses from the timer's speaker, all i need now is to get it send all of the 9v to the igniter so it can ignite the igniter.

igniter is in place of led and R1, all other res values are 1K, but the res with the red arrow next to it is 2K2.
 
Only the PNP is between the power source and your ignitor, so there will only be a 0.6V drop leaving you 8.4V, I can hardly believe this causes it to fail...

How much current does your ignitor require and what transistors are you using (type numbers)?
and can you draw how you connect the buzzer to the circuit?
 
The igniter goes off fine with a 'ok' 9v, meaning the 9v is not new but is also not at all dead. I'm sorry but i don't know the exact voltage. The only theory i can come up with is that the PNP also takes away a lot of the amps from the 9v, causing it still to retain its voltage but not causing the resistance needed in the nichrome to generate any heat. One thing that is a little weird is that when i tried to test this circuit (with the igniter) the latching seamed to turn off because of the short in the circuit (by the igniter), this even happend when i used a different powersource for the circuit and just used a transistor, in place of the LED&res, to switch a 9v to igniter only circuit on. Its almost like full 9v current through a transistor turns the transistor off for a time.

anyway, here is the circuit with the 9v power supply that i modified from the previous circuit:
 

Attachments

  • circuit_174.jpg
    circuit_174.jpg
    16.2 KB · Views: 1,003
I wouldn't use a emitter follower for this, but you can always try it...
But it needs to be connected diffirent, as it is now you're just shorting the speaker output out. 1 of the speaker outputs should go to gnd.

You say the latch turned of when you tried it with the ignition. There can be many reasons for this. Maybe your power supply can't supply enough current and goes 'trough its knees', making the voltage drop below the voltage required to keep the transistors on. Maybe the ignition requires more current then the PNP you use can handle...
Knowing the current required for the ignition would realy help.
 
Will a timer circuit work for you? This is a timer that will wirk on 9v fine. It will trigger the igniter. Just put the Igniter in place of the relay.
 

Attachments

  • delayed_on_timer.jpg
    delayed_on_timer.jpg
    12.6 KB · Views: 853
I already have the timer, all i need is a simple circuit to ignite the igniter when the timer starts to beep. And i really don't want to give the timer up, it can go up to 99:99 and is accurate and programmable to the second :D

the only problem is it beeps at the end, which complicates things for igniting stuff.

The best i can tell you, Exo, is that the igniters i use probably will go off with a little more voltage than the estes igniters. lets just says thats a 9v batter at full charge. i need some way to short the 9v over the igniter. one way i was thinking is too use a 1.5v button battery to operate the latching circuit. then somehow get that to flip a relay thus shorting the 9v over the igniter. this, i know, can ignite the igniter (relays work!). problems: 1.5 can't fip the smallest relay i can get: 5v relay, and i don't want another battery because the timer can function on a 1.5 button batt and i don't have the room for another.

another way is to put a not gate on the latching output, this can be used to hold a 5v relay 'on', powered by the 9v through a resistor, while the latch is 'off', then when the latch turns on the relay turns off and then shorts the full 9v through the igniter. (i like this idea, but it requires more space than i think i have...) problems: i waste some of the 9v's power holding the relay, when i want to save all the energy from the 9v to ignite the igniter.
 
Here is a simple SCR Latch circuit.
 

Attachments

  • scr_latch_circuit.gif
    scr_latch_circuit.gif
    3.7 KB · Views: 1,004
thats....exactly what i want to do....and its simple! THANKS HWW

now...this idea of a "latching relay" interests me...how exactly do you go about modifying a regular one to become latching. i think i know how but i just want to be sure... but the button 1.5v can't fip the relay...so a transistor arangment should do that... i need to do more testing
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top