Hi, I designed (but never used) this timer circuit to control the fans in my PJ.
I'm just putting it here in case it's of some use to someone.
Click to view attachment
R1 consists of a variable resistor and a fixed resistor. And allows you to control the time period the fans stay on for. The circuit is triggered when it's own power supply is connected.
To determine your timing components (R1 and C1) use this formula:
T (Time period) = R1 * C1
Remember, R1 is actually the VR + the Fixed Resistor value added.
Full Version: Helpful Timer Circuit I Designed
Lumenlab > LLAVS: Lumenlab AVS > Advanced Projector Builder > Technical Drawings, Designs and Templates
Thanks for the share.
This might be better suited to the "Technical Drawings, Designs and Templates" section of the forum.
Perhaps a Mod can move it.
This might be better suited to the "Technical Drawings, Designs and Templates" section of the forum.
Perhaps a Mod can move it.
Nice, good old 555 timer circuit. Looks pretty much standard.
QUOTE (SupraGuy @ Apr 11 2008, 04:09 PM) 
Nice, good old 555 timer circuit. Looks pretty much standard.
Yep. Nothing special, just thought it may come in handy for some people who aren't familiar with these kinds of timers.
Just a question, but is this your entire power circuit?
It looks to me that your SMPSU and Lamp have mutualy exclusive on states, unless I'm reading something wrong.
Or do you have a seperate power supply for your fans and for your controller?
I'm just wondering because I was planning on using a thermal switch to keep my fans on, but I might like this timing
thing, and while I can come up with my own design, I am wondering if there are concerns you though of that I didn't.
Also, I am assuming that is a relay in the center, and from what I can read it is switching from on to on basically.
It looks to me that your SMPSU and Lamp have mutualy exclusive on states, unless I'm reading something wrong.
Or do you have a seperate power supply for your fans and for your controller?
I'm just wondering because I was planning on using a thermal switch to keep my fans on, but I might like this timing
thing, and while I can come up with my own design, I am wondering if there are concerns you though of that I didn't.
Also, I am assuming that is a relay in the center, and from what I can read it is switching from on to on basically.
Eponymous hasn't been on since May, and may not be checking back in here anymore...
You're right though that there seems to be some wierdness with the relays. I understand what it is that he WANTED to do with them, I think, but they weren't drawn quite right.
From what I can see...
The SMPS should have full-time power, and NOT be controlled by the DPDT switch. Therefore the lamp switch can be a SPST switch. I would still put a master switch before that, for myself. That's me.
The relay in the center is obviously supposed to trigger the fans until the 555 timer circuit runs out, and yet allow them to be on whenever there is power.
This changes a couple of things though.
1. There needs to be a "trigger" to the 555 timer circuit to tell it when the lamp has been powered off. For this, I might be tempted to use a photocell and a NAND gate chip, but that could also be considered needless complexity. Set the output from the photovoltaic to the "reset" pin. This means that as soon as the lamp comes on, the circuit will reset, now being ready to operate in cooldown. When the light turns off, the NAND of the photovoltaic is sent to the trigger. As long as the ciruit has been reset, this then operates the fans from the "cooldown" power supply.
Complicated, and somewhat needless.
What this circuit really needs is 2 12VDC supplies Neither shoud need to be a SMPS, though that might be a good idea for the "main" circuit which will run the LCD supply. The other for the timer circuit can be a simple plug-pack, since it will never need to supply much current.
I should probably do up a schematic for what I'm thinking about, it's rather different from this after all...
You're right though that there seems to be some wierdness with the relays. I understand what it is that he WANTED to do with them, I think, but they weren't drawn quite right.
From what I can see...
The SMPS should have full-time power, and NOT be controlled by the DPDT switch. Therefore the lamp switch can be a SPST switch. I would still put a master switch before that, for myself. That's me.
The relay in the center is obviously supposed to trigger the fans until the 555 timer circuit runs out, and yet allow them to be on whenever there is power.
This changes a couple of things though.
1. There needs to be a "trigger" to the 555 timer circuit to tell it when the lamp has been powered off. For this, I might be tempted to use a photocell and a NAND gate chip, but that could also be considered needless complexity. Set the output from the photovoltaic to the "reset" pin. This means that as soon as the lamp comes on, the circuit will reset, now being ready to operate in cooldown. When the light turns off, the NAND of the photovoltaic is sent to the trigger. As long as the ciruit has been reset, this then operates the fans from the "cooldown" power supply.
Complicated, and somewhat needless.
What this circuit really needs is 2 12VDC supplies Neither shoud need to be a SMPS, though that might be a good idea for the "main" circuit which will run the LCD supply. The other for the timer circuit can be a simple plug-pack, since it will never need to supply much current.
I should probably do up a schematic for what I'm thinking about, it's rather different from this after all...
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