Well it all started a month or so ago. I had a call from one of my Distributors saying he had a little project for me.
Design spec was to make an LED flash. Not a problem I thought and went over for a meeting.
LED was initially a 1W Luxeon - still not a problem. Housing for project was smaller than Luxeon - ok - problems start
Maximum size of PCB which had to include the batteries (3 button cells), a switch, the flashing circuitry and the LED was now restricted to 40mm by 19mm - by the time I mounted 3 x SR41 cells on with the holders there wasn't much room left.
Found a 5mm LED which gave the correct viewing angle for the project and knocked up a flip flop out of transistors. Prototype looked feasible so we went out and bought some dedicated MT flasher ICs in a TO92 package. With a on/off ratio of 7:1 the batteries should last around 6-8 hours.
Knocked up some "semi-final" prototypes and my Distributor presented them to his customer who didn't like the flash rate. He wanted 5 seconds on and one second off with the option to change it. Bang go the nice easy MT chips.
Now - how to get 6-8 hours usage from 3 x SR41 cells (around 30mah) driving a 25ma white LED .......
Oh did I mention it had to fit in a tube so height was severely restricted ? The three button cells only just fit into the tube on one side of the board.
Currently working on using a 10F200 with the provision of PWM to try and maximise the battery life, bi-colour/tri-colour LED driving, automatic power off, various flashing patterns and if I have the space I'll try and make the flaming thing play Dixie as well
Don't you just love it when the goalposts keep moving
Design spec was to make an LED flash. Not a problem I thought and went over for a meeting.
LED was initially a 1W Luxeon - still not a problem. Housing for project was smaller than Luxeon - ok - problems start
Maximum size of PCB which had to include the batteries (3 button cells), a switch, the flashing circuitry and the LED was now restricted to 40mm by 19mm - by the time I mounted 3 x SR41 cells on with the holders there wasn't much room left.
Found a 5mm LED which gave the correct viewing angle for the project and knocked up a flip flop out of transistors. Prototype looked feasible so we went out and bought some dedicated MT flasher ICs in a TO92 package. With a on/off ratio of 7:1 the batteries should last around 6-8 hours.
Knocked up some "semi-final" prototypes and my Distributor presented them to his customer who didn't like the flash rate. He wanted 5 seconds on and one second off with the option to change it. Bang go the nice easy MT chips.
Now - how to get 6-8 hours usage from 3 x SR41 cells (around 30mah) driving a 25ma white LED .......
Oh did I mention it had to fit in a tube so height was severely restricted ? The three button cells only just fit into the tube on one side of the board.
Currently working on using a 10F200 with the provision of PWM to try and maximise the battery life, bi-colour/tri-colour LED driving, automatic power off, various flashing patterns and if I have the space I'll try and make the flaming thing play Dixie as well
Don't you just love it when the goalposts keep moving