If it's for one off or field calibration could you bring out a couple of=20 pins for a serial link to a laptop ? Maybe a simple USB serial interface ? You could sell it as "real time monitoring" or similar to your client and=20 get away with a bit of extra programming and a USB connector. Even an externally powered display with a serial interface on which field=20 engineers could carry round and plug in could work depending on exactly wha= t=20 the application is for. Dom ----- Original Message -----=20 From: "Dwayne Reid" To: "pic microcontroller discussion list" Sent: Friday, September 21, 2012 8:54 PM Subject: [EE] Need low-cost & small display > Good day to all. > > I have just finished the redesign of one of our older products for a > long-time (and valuable) customer - and now I'm being asked to make > more changes. The version just finished will go into production but > I need to start on the new version. > > This is a control board in a HVAC application and runs from > 24Vac. There is 120 / 240 Vac switching on one end of the board and > all of the low-voltage electronics is at the other end of the card. > > The card includes a sensitive differential pressure sensor which is > used to control the blower speed. The plenum pressure changes > according to which mode the system is currently operating in: > fan-only, heating, cooling. Pressure adjustments are made using > fairly expensive 3-turn trim pots (3 pieces, one each for cool, heat,=20 > fan). > > We want to get rid of those expensive trim pots and instead use > up-down programming buttons in conjunction with an on-board > display. I need an absolute minimum of 3 numeric digits but would be > really happy if I can find a low-cost alpha-numeric display of at > least 8 characters. A one-line display would work but a two-line > display would allow for some eye candy (a simple menu system, for=20 > example). > > The current power supply is a simple half-wave rectifier (fed from > 24Vac) with series resistor feeding a reservoir cap (sits at about > 24Vdc) followed by another series resistor feeding a 5V zener diode > regulator. Because I want to keep the wasted heat at a minimum, the > current 5V supply is fairly limited as to how much current that it > can supply. That pretty much rules out any form of 5V LED-based > display, unless I change that 5V supply to a buck SMPS of some sort. > > I see a few options - but they all sound to be more expensive than my > customer wants to spend. But I'll toss them out here in hopes that > someone can suggest alternatives. > > 1) 3- 7 segment displays running from 24V rail. Means that I have to > use something like 1 or 3 TPIC6C595 shift registers (which can handle > the 24V rail). One SR if I multiplex the displays, 3 if I don't. > > 2) standard intelligent LCD display module. Quite frankly, this > would be my preferred method but I just can't seem to find any > low-cost but tiny modules. Suggestions would be greatly appreciated. > > 3) one of those incredibly nice Organic LED graphic modules as seen > on the Gabotronics Xprotolab modules. His BOM gives it a part number > of UG-2864HSWEG01 and he sells them for $10 each. The downside with > using one of these are: need more PSU current than I have available > and needs a processor with much larger pin count than I am using > now. Neither of these is a killer but I'm looking for > alternatives. I'd also be interested in finding a reliable low-cost > source of these. > > 4) bare LCD glass. Needs a different, much larger PIC than I am > currently using (or a small PIC and lots of shift registers). > > Any suggestions? > > Many thanks! > > dwayne > > --=20 > Dwayne Reid > Trinity Electronics Systems Ltd Edmonton, AB, CANADA > (780) 489-3199 voice (780) 487-6397 fax > www.trinity-electronics.com > Custom Electronics Design and Manufacturing > > --=20 > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist=20 --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .