| Electronics > Projects, Designs, and Technical Stuff |
| 16 bit to 4 digit 7 segment decoder |
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| SiliconWizard:
--- Quote from: obiwanjacobi on January 28, 2020, 06:27:11 am ---Don't I need P-Channel here: low-side/cathode? --- End quote --- Nope? |
| obiwanjacobi:
--- Quote from: SiliconWizard on January 28, 2020, 07:44:07 pm --- --- Quote from: obiwanjacobi on January 28, 2020, 06:27:11 am ---Don't I need P-Channel here: low-side/cathode? --- End quote --- Nope? --- End quote --- ;D Thanks, I looked it up again. Is there a smaller ULN2003. Not 7 darlingtons but less, 4 (or 2x2)? |
| Buriedcode:
Am I missing some kind of design restriction here or do you just need something to drive the common cathodes of the segment display? Jellybean NPN transistors with base resistors will do just fine. 2N7000 will also work. |
| SiliconWizard:
Yeah frankly, you're dealing with < 100mA of current here. You can use any small NMOS directly driven by a GPIO. You can add series resistors to the gates for good measure, but even that could be done without... |
| macboy:
--- Quote from: obiwanjacobi on December 19, 2019, 08:27:08 am ---I have a (couple of) 4 digit 7 segment display module (NSB3881) and want to use it to plug into data and address buses of hobby projects to display bus values. The 7seg unit is common cathode and has all the segment lines (a-g/dp) connected over all 4 digits. I want to make a self-contained module with a 0.1" header that can be plugged into breadboards (5V logic). So I started to try to program a 2-digit version into a GAL22V10 (winCupl) but the segment mapping table generated too many product terms. My other thought was to use a cheap micro (preferably Atmel/AVR - don't know PIC and don't have the programmer for it) to read the bus signals and output the 7seg data for each digit. It would need 16 (bus data) + 8 (a-g/dp) + 4 (digit common cathodes) = 28 IO pins. (would like a reset and an optional latch too => 30 IO pins). Then I thought that perhaps there is a(nother) clever way to solve this problem and came here for inspiration. Suggestions? --- End quote --- I'd say ditch the old display modules and just buy something new. For around $1 you can get a 8 digit 7-segment display which is controlled serially using a MAX7219-alike controller. Then a small cheap micro like Arduino Nano (etc) has just enough I/O for the 16 bit input and to control the display. The extra digits could be used to hold min/max values, display voltage read from an A/D pin, etc. Or use the vertical segments to display the raw bits (4 bits per 7-seg digit). |
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