exxos's Atari, Amiga & retro forum

@exxos its almost like you were psychic.

PhilC wrote: 07 Oct 2020 22:15 @exxos its almost like you were psychic.

Or psychotic :roll: :lol:

PCB's came.. Hacksawed them into 4.. Bodged it onto the H5 power to test.. I think the LEDs are a bit dim on the green, need to find some better ones :roll: The LEDs actually turned on on the yellow ever so fractionally, but this may disappear once it is actually fitted in the keyboard as there is a series resistor anyway.. Not too worried about it overall anyway.. I think I got two versions of this board made different MOSFETs cannot remember but need to check...

Anyway, we have green yellow and off basically as expected :)

A re-spin of the board.. This one should turn the LED off fully, and I also added in a extra 220R in series with the yellow LED as it inherently seems brighter than the green. So hopefully this will even things out a little bit better.

Now I have woken up a bit I realise that the green LED going through the particular MOSFET I'm using, has a on resistance of around 200R.. I actually did that deliberately one respect to save having to solder a series resistor... On the motherboard side, I think it had 220R series resistance, so technically the LED should get the same current.. But in my testing I was just grounding the wire where it had 220R less resistance..

In any case.. The new board has 220R in the VCC line (which goes to both LEDS) . The green LED is the series resistance of the MOSFET (about 200R) . I also have now the addition of 220R in series with the yellow LED. Basically each LED will get exactly the same current at this point..

Now if the yellow LED is still too bright, actually on the keyboard ( or somewhere at least) I think there is a 220R in series with the keyboard yellow LED anyway.. So this will lower the current a little bit more to the yellow LED if it is too bright, but if it is too dim, that resistor can just be bridged over.. It is really difficult to know what will happen until the whole circuit is built and tested properly.