And my timer build begins...

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alaskanb3arcub
 
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And my timer build begins...

Post by alaskanb3arcub »

I bought a small Westclox(26630) alarm clock to turn into a interval timer, now I'm trying to determine just how much I have to replace. The first task, I figure, is to see if I can use the display inside, and wire in a backpack without the display module. However, I'm not sure how to figure out if I can use it or not. the following are the 2 part identifiers I could find:

https://photos.app.goo.gl/HX7GaedcM2qMEa7r6
https://photos.app.goo.gl/VRW4Rz95sC2g4enGA

Anybody else have success identifying the particular part? Alternatively, how I determine compatibility using a multi meter?

Thanks much!

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adafruit_support_mike
 
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Re: And my timer build begins...

Post by adafruit_support_mike »

Neither of those will be standard part numbers. The second one looks like a date code, indicating a revision from December 9th 2007.

It looks like a basic LED display though. If so, you should be able to reverse engineer the connections with a 5V power source and a 1k resistor:

Connect the GND line to a solid probe and the 5V line to one end of the resistor. Hold the probe against the first solder joint on the display and sweep the free end of the resistor along all the other joints. Then move the probe to the next solder joint, sweep them all with the resistor again, and so on.

The 1k resistor will limit current to the point that you won't damage anything, and if you do have simple LED connections, you'll see something light up when you get the right combination of 5V at the anode and GND at the cathode. If lots of LEDs light in sequence as you sweep the joints with the resistor, it's a common-cathode display. If only one LED lights per sweep, it's a common-anode display.

It doesn't take long to figure out a display and map the connections that way.

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alaskanb3arcub
 
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Re: And my timer build begins...

Post by alaskanb3arcub »

No resistors on hand. would 3v via a 2 AA cell holder work? I do have a multi meter, though. Also, there is no clear indication of ground that I can find.

https://photos.app.goo.gl/WhqDtiVg1VvnfU8L8

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adafruit_support_mike
 
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Re: And my timer build begins...

Post by adafruit_support_mike »

You need some kind of resistor.

LEDs, like all diodes, have an exponential voltage-to-current relationship. Increasing the voltage across one by about 60mV increases the current flowing through it by about 10x. Even small changes in voltage can increase the current enough to kill an LED.

AA cells can deliver up to 2A, and a pair of them will have much higher voltage than is necessary to light the LED. You'd identify the LED connections as they burned out.

Resistors limit the amount of current that can get to the LED. The voltage-to-current relationship for a resistor is linear, so doubling the voltage across one doubles the current flowing through it. If you put a resistor and an LED in series, then change the voltage across them, most of the change will appear across the resistor instead of across the LED.

If you have a box of old electronics to salvage, check to see if something has a through-hole 1k resistor you can pull.

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