I have an easy project but if you have enough experience about it.
-I have a led which typical forward voltage 2VDC and current value is 20mAh.
-I need to drive this led at the different brightness levels. And the levels will be changed by pushing a tact switch. And I have to lock tact switch by pushing 3 seconds and unlock by pushing 3 seconds and pushing 5 seconds to turnoff/turnon the led. So apparently i will need a microcontroller.
-The most important part is that the lowest power consumption is the key point of this product. For example, the lowest power consumption of a similar product is 4uA yes 4 microampere.
-The system supplied by CR2032(3V).
-Could you suggest a appropriate soluiton for this challenging project? Which microcontroller should i use? Maybe additionaly i should use a led driver i don't know. I don't want to restrict your idea.

 

We have done this project several times.
For the micro, You are looking for a 8 or 6 pin micro. I had to make the board about the size of the battery. Look at MicroChip or AVR or there are many companies that have very small low power micros. Choose one with an internal clock. Look for low power mode. Look at the PIC10Fxxx and PIC12Fxxx series also AtTiny85V-10. Because there is no reason for "fast" run the micro at a low clock speed to save power. You can even have the micro in sleep mode most of the time to save more.

Brightness of the LED. One option is to have the LED on 100% of the time for most bright and 25% of the time for dim and 5% for dim, etc. If the on/off time is above 100hz the eye will not see blinking.

If price is most important use a resistor to get from 3V of the battery to 2V of the LED and use a I/O pin to turn on/off the LED. You will loose 1/3 of the power to the resistor. If low power is most important then there are other options.

 

Is this a school related assignment?

 

For the lowest power LED power consumption you could use a simple (hysteresis type) buck converter configuration that uses an inductor and no series LED current-limiting resistor.
The converter duty-cycle can be controlled by the microprocessor.
That should typically give efficiencies around 90% while controlling the LED brightness.

 

Is this a school related assignment?

No it is related about my job. The company that i work have a product which power consumption is 50 uA and they want me to decrease to 4 uA.

 

We have done this project several times.
For the micro, You are looking for a 8 or 6 pin micro. I had to make the board about the size of the battery. Look at MicroChip or AVR or there are many companies that have very small low power micros. Choose one with an internal clock. Look for low power mode. Look at the PIC10Fxxx and PIC12Fxxx series also AtTiny85V-10. Because there is no reason for "fast" run the micro at a low clock speed to save power. You can even have the micro in sleep mode most of the time to save more.

Brightness of the LED. One option is to have the LED on 100% of the time for most bright and 25% of the time for dim and 5% for dim, etc. If the on/off time is above 100hz the eye will not see blinking.

If price is most important use a resistor to get from 3V of the battery to 2V of the LED and use a I/O pin to turn on/off the LED. You will loose 1/3 of the power to the resistor. If low power is most important then there are other options.

Thank you for your answer ronsimpson. You are right, the product that i said which power consumption is 4uA one uses PIC12Fxxx series. But first of all i have something to try. I have a circuit which has a STM32L0 series microcontroller. Power consumption about 50 uA but as you mentioned software dont use low power mode. I will try it Monday and update the result here.

 

For the lowest power LED power consumption you could use a simple (hysteresis type) buck converter configuration that uses an inductor and no series LED current-limiting resistor.
The converter duty-cycle can be controlled by the microprocessor.
That should typically give efficiencies around 90% while controlling the LED brightness.

Hmm i want to ask you something then because i dont know how a hysterisis type buck converter work. How this converter controls the brightness of the led? Does it limit the current or adjust the voltage or how? Thanks so much for your answer.

 

STM32L0 may be overkill for your application.
There are ultra low power MCUs that draw 20nA in sleep mode and 9nA in deep sleep mode.

 

STM32L0 may be overkill for your application.
There are ultra low power MCUs that draw 20nA in sleep mode and 9nA in deep sleep mode.

That has to be the understatement the year.

A 32-bit micro to control one LED!

Bob

 

I have used some 4 bit computers but there is not really a advantage.
Many little computers, you can set up a counter to wake up every 1mS and be in sleep mode most of the time.
Some computers have a pin that will force a wakeup. This is the pin to put a switch on. Some devices the current draw was so low that we did not have a power switch. The product left the factory with the battery connected.

On some products, we studied brightness verses battery voltage. We measured battery voltage and dimmed the LED a little when the battery is new and compensated a little as the voltage dropped. On other products we measured the LED current. On many we just let the LED dim as the battery went down. (things to think about)

 

i dont know how a hysterisis type buck converter work.

Google will give you many references.

Does it limit the current or adjust the voltage or how?

It rapidly turns a transistor on and off to control the current by varying the on-time versus the off-time.
The inductor smooths the pulses to give the average current of the pulses.

 

What is your hardware budget like?

 

What is your hardware budget like?

There is no budget actually. Only the limitation is area and the limit is 20mm diameter because of the diameter of CR2032.

 

Then microcontrollers are still on the menu. By the way, there are some really small microcontrollers available. If you don't need much I/O you can try one of the controllers in a SOT-23 package, like the Microchip PIC10F202 and the Microchip ATtiny24.

 

Then microcontrollers are still on the menu. By the way, there are some really small microcontrollers available. If you don't need much I/O you can try one of the controllers in a SOT-23 package, like the Microchip PIC10F202 and the Microchip ATtiny24.

Thank you for your suggestion. The main expectation is power consumption but your solution seems cheaper and suitable also.

 

You will often find that for a given process (family of parts) the parts with the smallest memory and fewest peripherals need the least current while idling or sleeping. Happily those are usually the less expensive parts in the family.

 

I was just at MIcrochip.com and they said the ATtiny uses more power than the PIC10F. While digging into the PIC10F202, which I have used, they suggested the PIC10FL320 as a newer version.
The "FL" is a low voltage version.
Use the 32khz oscillator which saves power.
Turn off as many features as possible. Everything pulls power and most can be shutdown.

I cannot find it now but somewhere I have some boards like this. They really help the development.

 

I was just at MIcrochip.com and they said the ATtiny uses more power than the PIC10F. While digging into the PIC10F202, which I have used, they suggested the PIC10FL320 as a newer version.
The "FL" is a low voltage version.
Use the 32khz oscillator which saves power.
Turn off as many features as possible. Everything pulls power and most can be shutdown.

I cannot find it now but somewhere I have some boards like this. They really help the development.
View attachment 262626

Hmm PIC12LF1571 is used at the equivalent product that i said. So this xlp series PIC should be the most suitable choise then. But it is very hard to find because of the chip crysis.

 

But it is very hard to find because of the chip crysis.

I am building based on what I can find.

 

Thank you for your answer ronsimpson. You are right, the product that i said which power consumption is 4uA one uses PIC12Fxxx series. But first of all i have something to try. I have a circuit which has a STM32L0 series microcontroller. Power consumption about 50 uA but as you mentioned software dont use low power mode. I will try it Monday and update the result here.

Hello ronsimpson. As i said i tried to reduce the power consumption but i can only reduce till 40uA. Because of that reason i gave up to try with STM32L0. As you can see attached file, I bought an evolution board via internet and waiting for it to arrive. The Manufacturer Product Number is AC103011. As you recommended i will try to continue with PIC10LF322. I am trying to learn PIC programming. Also i bought and waiting a PICKIT3 too. I will inform you thanks.