Digit1 was showing a slight ghost image of digit2. Turned out it is caused by a little leakage (1.2mA) coming through from the 2nd transistor.
I was using a 1K resistor on the base of both transistors.
I fixed the problem by usink 1K on transistor 1 and 3.3K on transistor 2. There is now no ghost image, and only 0.03mA difference in current on the 2 displays.
I will add that to my drawing, I expect Mike do the same.
Thanks for the feeadback.
The other problem I am having, is some slight interference- the display is good but every so often it misreads for a milisecond. The true reading is obvious, but if it continues (I'm hoping its due to oversized, undershielded prototype), I might need a firmware update.
It could be em noise as you suspect, keep us posted.
Would it be possible for the display to update less often, but update with the most common result (ie- if it read over a period of time CCCC
DCC
DCCCC, it would ignore the
D and just read out C?
If the program only refreshed the digits that have changed since the last update, wouldn't the 'unrefreshed digits go blank or very dim?
I'm not asking for someone to do that for me- just want to know it's possible before making a proper PCB.