Basic Stamp Help!!

SNAKExBITE

Im trying to make a countdown timer using 4 seven segment displays. I want to run them of the REV C board of education. Can anyone help me do this?

Franklin

Show us your circuit, links to the parts you are using and the code you have so far. We can help you but you have to do some of the work.

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- Stephen

SNAKExBITE

thats just it, have only done the project with the microcontroller that uses only one 7 segment display. I just need help on how to get started!

Mike Green

The best way to do a multi-digit LED display is to use a display driver chip like the one shown in Nuts and Volts Column #127:

www.parallax.com/Portals/0/Downloads/docs/cols/nv/vol6/col/nv127.pdf

The reason for using a chip like this is that the Stamp I/O pins can't drive multiple 7-segment displays without external transistors and, once you have a couple of transistors and resistors, it's getting to be easier to use a single LED driver like the one shown in the Column.

If you still want to use discrete transistors, you connect the display segments just like you did with the single 7-segment display, with each segment (a,b,...) from the 4 displays connected to the same I/O pin. You then need a driver transistor and base resistor similar to what's shown in Nuts and Volts Column #6. The type of transistor and how it's connected depend on whether you have common-anode or common-cathode displays.

You already have code to display digits on the single digit display. For 4 digits, you turn on one display driver transistor at a time, output the segment information, then turn off that transistor and repeat the same thing with the next digit. It's called multiplexing.