555 timer circuit help

[budm]

Re: 555 timer circuit help

Well, if the plug is open then there will be no Plug OK indicator (Green LED), so the plug is not going to draw the current but the relays and the timer will be drawing the current, and when the replay is off after 10 seconds, the timer will still be drawing current which your Green LED is not going to show you that because you do not have any current sensing device to see if there is current being drawn from the battery, so another added circuit.

[garry7263]

Re: 555 timer circuit help

The timer wont draw that much current when it is not activated. Maybe it is possible to use a momentary switch to activate a relay that will supply current for the 10 seconds, then when the timer goes out, it cuts power completely to the circuit?

[garry7263]

Re: 555 timer circuit help

Meaning that when you power the circuit on by pressing the momentary switch, it automatically drops the voltage to pin 2 to turn the timer event on, then when the even plays out, it cuts its own voltage to the relay and shuts off completely.

[budm]

Re: 555 timer circuit help

Well, it is another requirement that should be on the list.
So how are you going to solve the power problem if all you have is the 5V power supply, that is your big problem, you do not want to waste power, do you?

[garry7263]

Re: 555 timer circuit help

The battery I use for the flight pack is a 7.2 Li-Po battery using a switching BEC to put out 5 volts. They are 45c batteries are capable of pulling about 80 amps current and hold 2200mah. Cant drain the batteries below 3.2 volts though without damaging them. I have been flying with this set up for a long time and only have to recharge once a week. I use Li-Po battery of the same capacity in my transmitter. Saves a lot of charging time.

[budm]

Re: 555 timer circuit help

The battery I use for the flight pack is a 7.2 Li-Po battery using a switching BEC to put out 5 volts. They are 45c batteries are capable of pulling about 80 amps current and hold 2200mah. Cant drain the batteries below 3.2 volts though without damaging them. I have been flying with this set up for a long time and only have to recharge once a week. I use Li-Po battery of the same capacity in my transmitter. Saves a lot of charging time.

Well as I already indicated, you will be wasting 10W of power for what ever how long the plug stays on, if that is not a concerned to you, then use the linear regulator with BIG heatsink to dissipate the heat from the regulator so it does not burn up, so more weight due to added heatsink and that is an added cost to your BOM.
Designing a product is full of compromised, it is a matter of what is acceptable to you or your customer.

[eccerr0r]

Re: 555 timer circuit help

10 watts for 10 seconds = 100 watt-seconds = 1.67 watt-minute = 28mWh of power... Might be OK to waste it, might not, dunno.

So, do we want to PWM the 5V to the glow plug?

[budm]

Re: 555 timer circuit help

10 watts for 10 seconds = 100 watt-seconds = 1.67 watt-minute = 28mWh of power... Might be OK to waste it, might not, dunno.

So, do we want to PWM the 5V to the glow plug?

Why not? If it meets his requirement, his budget. One more 555 or dual 555, caps, resistors, trim pot, power MOSFET, heatsink, etc.

[jiroy]

Re: 555 timer circuit help

The 555 is a pretty powerful chip but cannot handle 3 amps. IIRC it has a maximum output of about 200mA, and I don't think it can pass that at 5 volts.

Plus you have that LED in series which means 3 amps must pass through that due to KCL. You'll need a relay or transistor to pass that much current.

How are you detecting the filament failure? Should the filament failure LED be on, even when the button isn't pressed?

A schematic would be helpful.

Same thought jumping to my head , A relay is needed ...

[garry7263]

Re: 555 timer circuit help

I think that is all getting too involved. Here is a pic if the commercially available product. I see a timer, regulator, microcontroller, and a transistor. I dont think there is anything on the other side. I dont need the microcontroller. The the top right is the input and the left is the output. the other lead coming off that is the push button with a LED inside it. (My guess is black is ground, red is the switch, and yellow is the LED. I assume that large component is a 1.5 resistor?

I think without the microprocessor the footprint of this could be reduced. I dont need over protection, resistance across the filament, and 10 different ways of programming it. Just on for 10 seconds with a condition indicator.

I might just buy one and reverse engineer the microprocessor out of it.

Basically I want this without the microprocessor, and the lead with the button, and having two LEDs and button on the board.

I was thinking maybe a mosfet to trigger the glow plug and the opamp for the LEDs?

[eccerr0r]

Re: 555 timer circuit help

The "commercial" product is probably checking the heater when it's off, something that can be easily done with a microcontroller without you noticing it.

In fact it looks like the "microcontroller" is doing the switching directly. That can't be a generic part it looks, no idea what part number that microcontroller is?

[budm]

Re: 555 timer circuit help

I think that is all getting too involved. Here is a pic if the commercially available product. I see a timer, regulator, microcontroller, and a transistor. I dont think there is anything on the other side. I dont need the microcontroller. The the top right is the input and the left is the output. the other lead coming off that is the push button with a LED inside it. (My guess is black is ground, red is the switch, and yellow is the LED. I assume that large component is a 1.5 resistor?

I think without the microprocessor the footprint of this could be reduced. I dont need over protection, resistance across the filament, and 10 different ways of programming it. Just on for 10 seconds with a condition indicator.

I might just buy one and reverse engineer the microprocessor out of it.

Basically I want this without the microprocessor, and the lead with the button, and having two LEDs and button on the board.

I was thinking maybe a mosfet to trigger the glow plug and the opamp for the LEDs?

So what is the sup[ply Voltage for that board? 5V? And the output Voltage to the plug is???? And the price for that board is???
It has 5V regulator on the board so input must be higher than 5V, but you said you need 1.5V 3A for the plug, so how is that board being used for?
If you look real close, the output is connected to an inductor, and the other side is connected to that large IC big trace to handle large current, I have never seen micro controller that can output large current like that, the GND trace for that IC is also big, so more likely to be some kind of power switching device because as you can see there is no relay to supply the power to the plug.
What is the specification of that board? I would find out before buying so you will have some idea what can be done to it since you have low budget.