How to build this circuit.

[tomdtc]

This needs to fit in a housing about the size of a ink pen. 1 led light with a on/off switch thats a solid light when turned on then starts blinking after about 60 seconds until turned off.

 

[gophert]

It sounds like overkill but s single microcontroller can do this most easily in the smallest space. The size can get extremely small so you'll have to let us know if this is a diy project or something that automatic pick and place equipment will assemble.

How many of these do you need? One or thousands?

How will it be powered?

How bright of an LED do you need?

How fast does it flash (on time, off time)?

 

[tomdtc]

Hi, Thanks for responding. Its a diy project. The cost will determine the quantity. I was thinking a small watch type battery that would fit in the pen size cylinder. 1.5vdc I guess. A regular led should be good. The flash rate won't really matter. Is the microcontroller and power all this needs? What would the part cost about?

 

[gophert]

Hi, Thanks for responding. Its a diy project. The cost will determine the quantity. I was thinking a small watch type battery that would fit in the pen size cylinder. 1.5vdc I guess. A regular led should be good. The flash rate won't really matter. Is the microcontroller and power all this needs? What would the part cost about?

Once designed, plan for 1000 pieces...
$0.50 for the microcontroller,
$0.25 for the pcb
$0.25 for the LED
$0.50 for a decent battery
$0.35 for a microswitch
$0.30 for assembly
===============
$2.25/each

You'll need to plan for a 3v Lithium battery

 

[alec_t]

You will also need to have a programmer for the MCU.

 

[tomdtc]

Thanks for responding. I will get back to you later with a couple questions.

 

[audioguru]

I think two AAAA alkaline cells will fit in a pen. The LED can be a 1.8V flashing red LED plus a resistor to limit its current. Then no circuit is needed.
I found a 3.2V AAA size lithium cell but it is too fat to fit inside a pen.

 

[gophert]

I think two AAAA alkaline cells will fit in a pen. The LED can be a 1.8V flashing red LED plus a resistor to limit its current. Then no circuit is needed.
I found a 3.2V AAA size lithium cell but it is too fat to fit inside a pen.

He wanted the LED to stay on for the first 60 seconds and then start flashing.

 

[audioguru]

The 60 seconds staying on then flashing will be a lot more complicated and more expensive that just flashing all the time it is on. Also when the LED stays on then the battery life will be much shorter.

 

[gophert]

Yes, and the battery would last even longer and the circuit would be even less complicated if the LEDs would never need to turn on.

 

[Nigel Goodwin]

The 60 seconds staying on then flashing will be a lot more complicated and more expensive that just flashing all the time it is on. Also when the LED stays on then the battery life will be much shorter.

It's trivial to do regardless, an LED, a tiny PIC (they do six pin SM ones), one resistor (to limit the current to the LED) and the battery - plus a little simple software.

 

[picbits]

I did something very similar using a PIC 10F series in surface mount (very small), a bulk capacitor and some SR41 cells in series to give me some power - the LED when constantly "on" was actually PWM'd at a very high frequency with a low mark space ratio which meant the average current from the cells was pretty minimal but the LED appeared on and at a reasonable brightness. After a certain time, the LED would then go into a flash mode with a bright pulse every few seconds. My design brief was that the customer wanted it to last an average working day. We managed to get around a week out of the cells with the predicted usage patterns.

 

[tomdtc]

The circuit using a PIC 10F sounds great. Would this fit into a small cylinder? The cylinder could be a little larger than a pen. What all components are needed and what's the cost?

 

[gophert]

The circuit using a PIC 10F sounds great. Would this fit into a small cylinder? The cylinder could be a little larger than a pen. What all components are needed and what's the cost?

See post #4 above. I quoted the price of a PIC10-series. Price depends on quantity but about $0.35 to 0.45 each plus other listed parts (again, post 4).

 

[tomdtc]

What I'm looking for is a simple circuit to light a led after a 60 second delay. Ideally it would start via a thermal sensor at about 90 degrees. This is for a cooking device, and no it's not for drugs. It could shut off when removed from the heat source or a switch.

 

[ChrisP58]

What I'm looking for is a simple circuit to light a led after a 60 second delay. Ideally it would start via a thermal sensor at about 90 degrees. This is for a cooking device, and no it's not for drugs. It could shut off when removed from the heat source or a switch.

90 degrees what? Please note that this is an international forum so, since temperature is measured with different scales in different parts of the world, you need to specify which scale you're using.

The PIC10F320 has an internal temperature indicator. That should work unless you need to measure the temperature remotely from the chip. Then a thermistor may be adequate. What level of accuracy do you need?

How high of a temperature does this thing need to withstand? Not just in normal use, but if the chef gets distracted and something overheats?

https://www.microchip.com/wwwproducts/en/PIC10F320

 

[tomdtc]

It does not have to be that accurate. Its purpose is to start the timer. The temperature will reach around 115 celsius at the devise.

 

[ChrisP58]

There is a version of the PIC10F320 that goes up to 125°C. And you should be able to find high temp versions for most of the rest of the components.

The problem will be the battery. Typical max temperature for a Li-Ion cell is 60°C. There may be some high temp versions that may go a little higher than that, but going up to 115°C is very unlikely.

Other chemistries have different max temperatures, so you might find something to go up that high.

 

[Nigel Goodwin]

Funny how it's suddenly changed entirely, and got a LOT more difficult.

Use a separate probe, and keep the electronics out of it - there was never any mention of it needing to be water and heat proof.

 

[tomdtc]

I was not very clear about the application. There will be a metal rod that is subject to the higher temps. The components would be in a handle attached to that. And its not that funny, I just have an idea and exploring different options on how to make it so.