Adjacent Led lights up automatically - LED matrix - Page 1
Forum section: electronics / projects

author: LexLabs
author_rank: Contributor
timestamp: October 29, 2021, 01:20:16 pm
content: Hi, I've been working on this LED matrix, and when I light up an led, the adjacent led lights up dim automatically . What could be the reason?Note:I'm using D-latches for rows and columns.

author: capt bullshot
author_rank: Super Contributor
timestamp: October 29, 2021, 02:16:42 pm
content: Quote from: LexLabs on October 29, 2021, 01:20:16 pmI suppose you're using column / row multiplexing. If so, you'll have to implement some dead time when switching rows.So the sequence is:turn off all columnswait a bitselect next rowwait a bitturn on column LEDs to be lit on this rowand so on

author: perieanuo
author_rank: Frequent Contributor
timestamp: October 29, 2021, 03:44:48 pm
content: without schematics we can't guess

author: LexLabs
author_rank: Contributor
timestamp: October 29, 2021, 04:03:03 pm
content: Sure, also the fast switching causes light to dim very much. When the sweep is slow (around 100 milliseconds) the leds are brighter, when its fast (1 millisecond) it very dim. How can I compensate this??

author: mikerj
author_rank: Super Contributor
timestamp: October 29, 2021, 04:10:46 pm
content: You'll have to drive the LEDs harder (higher current) to get more brightness, though you'll probably need proper transistor (bipolar or MOSFET) switches for your row and column drivers to be able to do this. The datasheet for your LEDs should give you the maximum current for the time you enable them for, which is usually quite a bit higher than the steady state max current.

author: LexLabs
author_rank: Contributor
timestamp: October 29, 2021, 04:32:11 pm
content: Attached those hereBoard Control.pdf(200.45 kB - downloaded 64 times.)Board Array.pdf(343.74 kB - downloaded 110 times.)

author: perieanuo
author_rank: Frequent Contributor
timestamp: October 30, 2021, 10:17:57 am
content: i think what you did for cathode you must do for anodes current, seems the 74ls353 are overwhelmed by the LED total current.in English, like others pointed, provide more current for the leds, for me between U3-U6 drivers are missing.we don't now how much current your leds are eating, so again we can't advise correctly. don't worry, nobody steals a non-working project, anyway his difficulty level is not approaching that kind of level

author: LexLabs
author_rank: Contributor
timestamp: November 05, 2021, 05:08:00 am
content: Quote from: perieanuo on October 30, 2021, 10:17:57 amThis is what confuses me a lot, each leds need 20mA, and from the datasheet I could see that the 74HC573 provides a little over 20mA on each of its pins. I'm speculating that the dimming is due to the scan itself.UPDATE: I switched from Row scanning to Column scanning, it's way better now. I got to get rid of most of the ghosting leds by following capt Bullshot's suggestion. Still working on the brightness issue. when I scan slower (I.e. at around 1000ms) the leds are sufficiently brighter, when I increase the speed it gets dimmer.

author: StillTrying
author_rank: Super Contributor
timestamp: November 05, 2021, 07:30:53 am
content: "I switched from Row scanning to Column scanning,"Always turn off the transistor first because saturated transistors are slow to turn off.Wait 2us before enabling the next 74 outputs and/or next transistor.Unfortunately that 74HC doesn't have +/- 20mA outputs, you can't go byLimiting values,the data sheet doesn't say how much the outputs droop by when you go above 7mA. For more brightness you might have to reduce those resistors quite a bit.