Ok not Amps but parts of. Often we see and use the standard advice of 20mA, but seriously is that much needed? Personally i dont use anywhere near that these days. What got me thinking was two things mainly, on one micro board dev board i use alot it measures total current from the board.
The IDE and sensing on the board is capable of reading uA range easily. For this microbe cell i need really low power so i am using a ultra low current micro, i had the IDE current screen up and was measuring sleep states and current draw, the board has a tiny smd led on it thats seen easily when its lit, when i looked the entire board was running at around 1mA with the led included.
So i did some searching and you tube shows a photon meter and a led being lit at very low current ~500-600uA. The led was a normal 5mm cheapo red led, it wasnt bright by any standard but you could see it was on (just).
So looking at some the other boards i use i measured those, all use smd leds and there are various colours. Voltage is under 5V and the leds are plenty bright at 1mA.
So i swapped out some the smd leds and used 3-5mm leds (red,green,blue,white and RGB) all at 4V, i got decent brightness from all of them at just under 2mA (~1.7mA average). So generally what current do you aim for?
For most apps i admit it dosnt make much difference if run at 25mA or 2.5mA, but when your using really low power micro's or want/need long battery life or have low current sources, every mA counts, for the microbe cell i can get decent current density but the linear tech boost chips have pretty low max current inputs.
So this has given me a problem, the energy board i am using from linear tech has a max input of 20mA on the input i am using so i dont want to waste most of that on a led!
It does have a cap bank for storage and it allows the different harvesting sources to be diode Ored, so i am splitting the cathodes from the cell into several of the boards inputs and adding bigger cap storage bank. But i still think its worth saving what i can.
The other thing is the pic ports, some the newer chips have 20mA max output per pin and fairly low max port current, so why use 20mA on a led when 2mA seems plenty.
So just out of interest i wondered what current most design there leds to use in circuit and why. For those interested the photon counter video is a EEV blog one if you want to go check it out, shame they didnt use different leds though.
The IDE and sensing on the board is capable of reading uA range easily. For this microbe cell i need really low power so i am using a ultra low current micro, i had the IDE current screen up and was measuring sleep states and current draw, the board has a tiny smd led on it thats seen easily when its lit, when i looked the entire board was running at around 1mA with the led included.
So i did some searching and you tube shows a photon meter and a led being lit at very low current ~500-600uA. The led was a normal 5mm cheapo red led, it wasnt bright by any standard but you could see it was on (just).
So looking at some the other boards i use i measured those, all use smd leds and there are various colours. Voltage is under 5V and the leds are plenty bright at 1mA.
So i swapped out some the smd leds and used 3-5mm leds (red,green,blue,white and RGB) all at 4V, i got decent brightness from all of them at just under 2mA (~1.7mA average). So generally what current do you aim for?
For most apps i admit it dosnt make much difference if run at 25mA or 2.5mA, but when your using really low power micro's or want/need long battery life or have low current sources, every mA counts, for the microbe cell i can get decent current density but the linear tech boost chips have pretty low max current inputs.
So this has given me a problem, the energy board i am using from linear tech has a max input of 20mA on the input i am using so i dont want to waste most of that on a led!
It does have a cap bank for storage and it allows the different harvesting sources to be diode Ored, so i am splitting the cathodes from the cell into several of the boards inputs and adding bigger cap storage bank. But i still think its worth saving what i can.
The other thing is the pic ports, some the newer chips have 20mA max output per pin and fairly low max port current, so why use 20mA on a led when 2mA seems plenty.
So just out of interest i wondered what current most design there leds to use in circuit and why. For those interested the photon counter video is a EEV blog one if you want to go check it out, shame they didnt use different leds though.