{"id":4575,"date":"2024-01-28T14:59:39","date_gmt":"2024-01-28T13:59:39","guid":{"rendered":"https:\/\/www.heinpragt.nl\/?p=4575"},"modified":"2024-02-04T11:44:55","modified_gmt":"2024-02-04T10:44:55","slug":"eight-digit-seven-segment-display","status":"publish","type":"post","link":"https:\/\/www.heinpragt.nl\/?p=4575","title":{"rendered":"Eight digit seven segment display"},"content":{"rendered":"\n

When you want to clone a retro computer board like the MK14 or KIM you will need to connect a seven segment display array. This may also be very nice if you design your own standalone mini computer board. I was experimenting with a Tang Nano FPGA and also needed a display and that is when I decided to document what I made. This is a simple universal 8 digit seven segment display unit that can be driven by 8 (or 7) segment select lines and 8 row select lines. The idea is that you can multiplex the displays, so first select display 1 and output the correct segments, then select display 2 and output the correct segments and so on. If you do this at a speed of more then 50 times a second it will appear that all displays are stable and continuously displaying. This is a basic design you can use in your designs.<\/p>\n\n\n

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I use two 4 digit seven segments display units with common cathode (-) lines, but you can also use single or even 8 digit displays. You can also use 7 digits, in this case you will only connect the first 6 row select lines. To select a display we need a kind of switch, most MCU (or FPGA) chips are not capable of driving this current so we need a transistor to switch the display on or off. But I like the very handy, cheap and common Darlington-array ULN 2803 chip that is perfect for this job. The segements are drivern with a positive voltage for on and the rows als also selected with a positive level. You can use this design for 5V and also for 3V3 designs without any modification.<\/p>\n\n\n

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In the segment lines we need some way to reduce the current for the leds in out display and 470 Ohm is a very common value. You can lower or raise this value a little to make the displays light up brighter as you like. The ULN2803 is also very easy to wire on a breadboard, all the inputs are on one side and all the outputs on the other side, and compared to 8 transistors with a base resistor this chip takes up very little space.<\/p>\n\n\n\n

Have fun, regards, Hein Pragt.<\/p>\n\n\n\n

<\/p>\n","protected":false},"excerpt":{"rendered":"

When you want to clone a retro computer board like the MK14 or KIM you will need to connect a seven segment display array. This may also be very nice if you design your own standalone mini computer board. I was experimenting with a Tang Nano FPGA and also needed a display and that is […]<\/p>\n","protected":false},"author":1,"featured_media":4576,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[48],"tags":[133,134,135],"class_list":["post-4575","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-eng","tag-eight-digit","tag-seven-segment","tag-uln2803"],"_links":{"self":[{"href":"https:\/\/www.heinpragt.nl\/index.php?rest_route=\/wp\/v2\/posts\/4575","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.heinpragt.nl\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.heinpragt.nl\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.heinpragt.nl\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.heinpragt.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=4575"}],"version-history":[{"count":2,"href":"https:\/\/www.heinpragt.nl\/index.php?rest_route=\/wp\/v2\/posts\/4575\/revisions"}],"predecessor-version":[{"id":4604,"href":"https:\/\/www.heinpragt.nl\/index.php?rest_route=\/wp\/v2\/posts\/4575\/revisions\/4604"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.heinpragt.nl\/index.php?rest_route=\/wp\/v2\/media\/4576"}],"wp:attachment":[{"href":"https:\/\/www.heinpragt.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4575"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.heinpragt.nl\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4575"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.heinpragt.nl\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4575"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}