TIL311 spi display board - Page 1
Forum section: electronics / projects

author: Ketturi
author_rank: Regular Contributor
timestamp: November 07, 2017, 11:38:36 am
content: Hi, I am working on TIL311 led display board that converts 5 of these displays to SPI bus for easy connection to arduino etc.I have some of those retro 7-segment displays that come in DIP package and include internal decoding and driving logic (http://www.mouser.com/ds/2/588/til311-e4-519224.pdf). Those are bit hard to get nowadays and ebay prices have gone way up so this will be probably one-off project.I thought of getting some peer sanity check before spinning board from OSH Park. I've included board images and schematics as attachment.Oh and ground fill was bit of afterthought, I first routed grounds as separate tracks, and I am still not sure should i clean up those and just use ground fill with appropriate vias, or just use single tracks because fill is not that effective on cramped board. Those old displays are quite power hungry, max 900mA for all of them not including current for shift registers and decimal points so ground and power vias are probably too small and sparse.What do you think?

author: Ketturi
author_rank: Regular Contributor
timestamp: November 07, 2017, 01:14:55 pm
content: Here is slightly modified board without copper pours. Still not sure if I should use ground fill as it wants to create ground loops, this is not even high frequency application so I think I would get away with separate gnd traces. And I don't think EMC would be problem in one-off projects and prototypes anyway.

author: floobydust
author_rank: Super Contributor
timestamp: November 07, 2017, 06:01:41 pm
content: The TIL311 is a nice retro LED display, goes back to 1972.I looked at your design and have a few comments.The TIL311's have a built-in latch, so you can parallel the LED data bus D0-D3. This would save two HC595's (20->4 lines). You load the SPI latches with data for one digit, then pulse that digit's latch strobe. Right now, you can load all digits at once (but why separate strobes then?, you could use just one strobe for all).I would make the PCB a bit bigger to allow for screw mounting holes on the corners, and tolerate some slop on the width of the displays around +/-1mm each. They look very close to each other. If you are using larger 0.8mm PCB holes then there is some slop allowed.The HC595's are right up against the header. It's a bit tight.TIL311 max. is 45-90mA LED supply, so the traces are not critical. There is no multiplexing so EMI is mostly from the SPI bus.For aesthetics, I would use SMT headers so you don't have shiny solder pins visible on the display side.On some LED display boards, I have no silkscreen on the top layer, only the back side and dark black solder mask.Pimoronioffers a Raspberry Pi shield using similar Lite-On LTP-305 displays (LED only, no decode/driver/latch).

author: Ketturi
author_rank: Regular Contributor
timestamp: November 07, 2017, 10:21:30 pm
content: Thanks,Quote from: floobydust on November 07, 2017, 06:01:41 pmI am driving all displays with single strobe, which loads every digit at once from shift register output. There is Blanking Input connected to every display so I can shut them down individually, otherwise it would always show value on digit.QuoteTested those displays with perfboard and they will fit just fine at 2.54mm spacing and I do not want additional gaps between digits. It will be tight fit but everything should work. I will design and 3D print custom bezel around displays, that houses red filter glass and mounts to front panel. Front panel won't be much higher than PCB. The bezel will be just a bit wider than displays.QuoteThose dot matrix led displays are cool, at one point they really made advanced and sophisticated display elements before LCD's became cheap and customizable solution. I wanted to use those but I already had TIL311 displays and this application will just show numbers anyway.I am building desktop load meter that shows CPU load with old industrial analog gauge and memory usage with numbers. Those led displays fit right on the era of 70s industrial equipment, and I'm after the look of old nuclear plant control room.