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By brainwav
#137042
Does anyone know how to reuse the LCD displays with the rubber connector? I got a pedometer from the dollar store and took it apart to find what you see in the attached picture. It has 5 7-segment digits. I've tried googling it, but didn't find much on them. It has 14 pins, so I was thinking that 7 pins are used for the 7 segments, 5 for selecting one of the 5 digits, and a power and ground? I was measuring the PCB and was getting sometimes 50mV and 16mV.

I tried removing the epoxy, but ended up removing the chip/die. I will buy another one soon.

Thanks,
Denis.
By skimask
#137052
Probably only getting 50mV and 16mV because the segments are multiplexed.
If you start probing around with a multimeter using the diode check function (i.e. continuity), you should be able to figure out what goes where and draw out a diagram from there.
By MichaelN
#137064
You are presumably trying to measure DC voltage, but LCDs are driven with squarewave, which probably explains why you're not measuring much,

Anyway, I recommend you buy an LCD screen from Digikey / Mouser / Newark, as you could waste a LOT of time trying to figure out a screen without data. Not worth it to save a dollar or 2 IMO.
By brainwav
#137092
Yeah but, If I can figure it out, then I can just go down to the dollar store when I need one instead of driving far, or waiting a week for delivery. Plus it would keep the cost down. Are the liquid crystal displays driven differently than LED? like if I apply voltage, will the turn black?
By MichaelN
#137098
Yes, but dollar stores change their stock all the time - you could spend MANY hours figuring out the LCD and then never be able to buy one again. Waiting a day or so and paying a few more dollars for a product with a datasheet makes much more sense.

LCD and LED displays are completely different. Essentially yes, you can turn an LCD segment black by applying a DC voltage, but it's not done like this as the display would ave a very limited life. Instead, the LCD has a "backplane" and segments. The backplane is driven with a squarewave (I think a few tens of Hz); to turn a segment black it is driven with a squarewave which is out-of-phase with the backplane. To turn a segment off it is driven with the same signal as the backplane.

While certain microcontrollers have built-in support for driving LCDs directly, what you probably want is to buy a display that you can drive with a parallel / serial interface without worrying about the squarewave voltages.
By brainwav
#137102
Ok, so I will try to find an already made one. I looked at Digikey and Mouse, but could only find the display and not the controlling board. You said in previous posts that I was trying to save a buck or two. Where can I find these $3 displays?

Thanks,
Denis.
By rmteo1
#137103
brainwav wrote:Where can I find these $3 displays?
These standard 16x2 LCD displays are $3.13/each shipped.

Image
By MichaelN
#137106
brainwav wrote:... could only find the display and not the controlling board... Where can I find these $3 displays?
When you say the "controlling board" are you referring to just the control of the LCD display, or are you talking about a board that can be used for other functions? Displays such as that suggested by rmteo1 are an "easy" way to display alphanumeric characters, and use a parallel signal interface (4 or 8 bits wide). You still need to send them data of course.

What is your application? Will you be sending data to the display with an Arduino or similar? This can be an easy way to get started, as lots of code is already available.

Digikey has hundreds of displays that should be suitable. Try searching for "LCD" and then select "Display Modules - LCD, OLED Character and Numeric" from the search results. You'll probably want to stick with alphanumeric displays rather than graphical (which can be tricky to get working).
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By yourshoesareuntied
#137145
I don't necessarily see this project as just a way to "Save" money, to me I see it as an inexpensive way to learn how to hack, or reverse engineer an existing circuit. If your learning this art with Dollar Store stuff that's an inexpensive way to get started. I just may have to pick one up too.
By omagasohe
#137163
I'd second it if i had a logic analyser and some time on my hands. with out a way to tell how many lines change over time it's not as easy. if your serious about this hobby i'd spend the money i'd save on some test equipment. an o-scope and/or logic analyser would cut hacking time in half. spark fun sells some that are great for hobby use. and never under estimate the power of ebay. china has some great knock offs.
By brainwav
#137185
Basically I wanted it to be small and cheap. The ones that are linked above (~$3) are big and bulky. I have two, one with the sparkfun serial board and one without. The one I got from the dollar store is tiny and displays all the digits I need. I just needed to know how to control it. I'm planning to control it using a Mega8. There's no electronics in the display, it's mostly glass, so I should be able to just apply some kind of voltage (square wave or not) and get some results. I just have to figure out what pins are what.

Even if they discontinue this product or start to carry something different, they should all be controlled the same, you would just need to find the correct pinout again for that new lcd.

Denis.
By trialex
#137201
you would just need to find the correct pinout again for that new lcd
That's enough to justify a known LCD from my point of view, but I applaud your willingness to get it working.