Following on from Westaust55's thread;
"LED display for compass heading" http://www.picaxeforum.co.uk/showthread.php?t=9904
Have been investigating ways to effectively double the outputs of an I/O expander.
To recap, Westy came up with a nifty scheme to indicate 32 positions from 16 by showing combinations of 1 or 2 LEDs.
I would prefer to use 32 LEDs but don't want to install another I/O expander.
As the compass display will only ever light 1 LED at a time, I figured that if the 32 LEDS were split into 2 banks, then the supply could be switched from one bank to the other and utilise the same 16 I/O pins to achieve the 32 outputs.
As the LEDs are supplied with a PWM output rail (which is common to other displays and used to dim the LEDS) the I?O expander sinks current.
The PWM is provided to the loads via a P-Channel MosFet driven by the PICAXE pwm output.
Have only a single output available to control this switching.
So have some options to provide this switch;
1. a couple of transistors - not sure which or how to set up
2. a N-channel/P-Channel enhanced MOSFET pair - IRF7338PbF around NZ$3
3. DIL PCB relay - coil current issues
3. Photomos relay.
Have figured the photomos is probably simplest as it is very compact, next to no current required from the PICAXE port and the Panasonic AQV212 is configured equivalent to a single pole changeover relay in a 6pin DIP.
This will cost some NZ$9.00 however.
Any comments / alternatives / options appreciated.
"LED display for compass heading" http://www.picaxeforum.co.uk/showthread.php?t=9904
Have been investigating ways to effectively double the outputs of an I/O expander.
To recap, Westy came up with a nifty scheme to indicate 32 positions from 16 by showing combinations of 1 or 2 LEDs.
I would prefer to use 32 LEDs but don't want to install another I/O expander.
As the compass display will only ever light 1 LED at a time, I figured that if the 32 LEDS were split into 2 banks, then the supply could be switched from one bank to the other and utilise the same 16 I/O pins to achieve the 32 outputs.
As the LEDs are supplied with a PWM output rail (which is common to other displays and used to dim the LEDS) the I?O expander sinks current.
The PWM is provided to the loads via a P-Channel MosFet driven by the PICAXE pwm output.
Have only a single output available to control this switching.
So have some options to provide this switch;
1. a couple of transistors - not sure which or how to set up
2. a N-channel/P-Channel enhanced MOSFET pair - IRF7338PbF around NZ$3
3. DIL PCB relay - coil current issues
3. Photomos relay.
Have figured the photomos is probably simplest as it is very compact, next to no current required from the PICAXE port and the Panasonic AQV212 is configured equivalent to a single pole changeover relay in a 6pin DIP.
This will cost some NZ$9.00 however.
Any comments / alternatives / options appreciated.
Last edited: