[Moved]: 7 segment display questions

[chris78vette]

I have a board with 5 , 7 segment with decimal point running 3v - I would like to make an external display with larger 7 segments running on 9-12v .

The board I have uses 8 cathodes connected to the microprocessor and 5 transistors 1 per each 7 segment connected to the anode .

My question would be is there anyway to use a secondary power source to drive the external display and how I would get the input/output to the new 7 segments without damaging the old board ?

 

[BradtheRad]

You should not allow 9-12V to reach the microprocessor which is running at 3V. This also includes devices which are in contact with the 9-12V supply.

From the sound of it, you have a common-anode display. I guess you have five PNP transistors at the high side?

The idea is to run the displays in parallel. The large display needs additional transistors to drive it. I think you'll need to add an array of several more transistors, and perhaps inverting gates as well.

 

[crutschow]

Can you post a schematic of what you have?

 

[chris78vette]

Yes I think there are 5 pnp's on the high side , kinda backwards from my experience playing with microprocessors . I thought it should have been sending from the microprocessor . I will try to draw and post a schematic of what I have.