I've taken apart a cheap kitchen timer, and taken out the LCD. I want to try to drive it with an Arduino and shift register. I've heard that you don't want to use DC to drive these, so what voltage level of AC should one use? Also, are there any simple low voltage inverter circuits I could utilize for this?
Unless you can find a datasheet for that unit, you are just making shots in the dark. Toss it and buy one that has a datasheet.
tinkerkid:
I've taken apart a cheap kitchen timer, and taken out the LCD. I want to try to drive it with an Arduino and shift register. I've heard that you don't want to use DC to drive these, so what voltage level of AC should one use? Also, are there any simple low voltage inverter circuits I could utilize for this?
how is the unit powered ?
it it has battery, very good chance that it is a dc device.
post a pic of the unit, but be prepared to toss it for one that has data sheets on what connects to what and what power to use and such.
What kind of LCD?
The black text segmented digits like on most calculators? Red glowy segmented digits? Full rgb pixel LCD?
What is your interface? Loose end of a ribbon?
Help us help you. Not all of us have hacked into your webcam to see what it is you're talking about.
Yes, it is battery powered - a coin type battery to be exact. And it is black segmented text like on most calculators. I plan on soldering wires to the PCB traces in order to interface with the display, as I can't solder to the clear ribbon connector.
My guess is that one of the lines is a common ground, and the others all activate a segment. Is there a common voltage that is used to trigger liquid cryslals?
It looks like this
Would actually help if you posted the actual thing you're working with.
How many digits? How many lines in the ribbon?
I don't think it would work as you think, that would require 8 lines from each digit. It's definitely not how that display in the picture you showed works, but that's not what you're working with.
Looks like a drinks coaster to me. Or maybe a shim for that wobbly table.
This page says the LCDs use AC voltage
http://www.vintagecalculators.com/html/calculator_display_technology.html
we do not drive the LCD, we control the driver chip
that driver chip drives the LCD.
if you can find the data sheet for the LCD, , find the frequency, voltages and currents needed, you are part of the way there !
then you only need to write the code that drives the voltage/frequency !
an LCD on e-bay $1.55 free shipping.
http://www.ebay.com/itm/161104094300
call us lazy, but we take the easy route.
I think a 4-digit segmented display is more in line with the kitchen timer screen. And you can get like 2 of those for a buck. Just be mindful about common anode or common cathode to suit your setup/program/chip driver if you use one.
Thank you all for the responses. I have a ton of these laying around so I think I'm going to try to get them to work instead of buying something. I couldn't find a data sheet for my display, but I found that the operating voltage is usually no greater than 5v ac. To test this out and determine pins, should I build an inverter circuit?
And then get a driver, I assume, to use when interfacing with Arduino.
OP posted image.
A 7-segment LCD will often be just the glass, with connections for segments and a number of backplanes (often up to 4).
For 12 connections it have segments A to G and DP with 4 Common line.
Driving LCDs can be awkward since they don't use just two levels, so you can't drive them with common digital logic.
The best thing you can do is select a microcontroller with integrated LCD controller, which you can connect the display directly to, like the TI MSP430x4xx. Like most controllers this one also knows just segments; it isn't aware of digits or anything. (Great, first we had a dumb display, now we have a dumb driver as well!) There's reason for this. These LCD drivers are often used to drive custom LCDs which may be a mix of a numeric part, bar graphs and custom symbols. Such a symbol is also a single segment, so it makes no sense to talk about digits.
Further reading
MSP430x4xx Family User's Guide. LCD controller is covered on p.709 ff.
Using the MSP430 as display driver may be a good idea: your Arduino can stick to its main task, and the program for the MSP430 can be kept simple (if you don't have much experience with it) or advanced (if you want to make it an intelligent driver, which you can supply with commands like "increment").
Were these timers working before you broke them or did you just have a box full of broken ones?
Seems like getting them to display other things will invariably cost extra money. I'd probaby be more interested in salvaging them for buttons and timing crystals.
tinkerkid:
Thank you all for the responses. I have a ton of these laying around ...
Well, that's new information. If you can afford to destroy a few of them, then start experimenting!
If you have one working and you have an oscilloscope, you can explore the signals that it's sending to the LCD.