LCD USB Serial Backpack Not Working

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Tinkwithanr
 
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LCD USB Serial Backpack Not Working

Post by Tinkwithanr »

I've run into an issue with 3 of the LCD Serial backpacks, and it seems like the same issue on all of them. I'm working on a display for my car using the 16x2 Negative RGB LCD. After probably 20 or 30 power cycles (turning it off and on to test new code, or just turning the car on) the display stopped working properly, displaying jiberish or showing only solid blue or red for the backlight. Then after one more power cycle the lcd didn't power up at all.

After the first time this happened I unsoldered the backpack from the screen to determine which unit the problem was in. Wiring the lcd screen up the old fashion way made it power up fine. So I soldered the backpack to a new screen and that screen also failed to power on. The red power LED on the backpack does still light up in all instances, but the backlight of the LCD screen is not lighting up at all.

At first I though maybe my code was bad, so I ordered 2 new backpacks and hooked them up the same way as the first unit. They both worked for a while, but then displayed the same issue. So I'm fairly confident my code is alright, as is my wiring and soldering.

Any help you could give me would be greatly appreciated.

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adafruit_support_mike
 
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Re: LCD USB Serial Backpack Not Working

Post by adafruit_support_mike »

How are you powering the backpacks?

It sounds like a chip failure, but having three different units work then fail sounds a lot like they're being killed by something in the operating environment.

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Tinkwithanr
 
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Re: LCD USB Serial Backpack Not Working

Post by Tinkwithanr »

The backpacks, along with the Arduino Pro Mini I'm currently using, are given +5V from a fixed voltage regulator (1A max output, standard radio shack dealio, found here: http://comingsoon.radioshack.com/-5v-fi ... YI0iflVhBc). I'm powering that from the vehicles +12v swithced circuit with a 470mF cap across the input for decoupling.

Edit: Also, both circuits share a common ground.

Some more info:
-One of the backpacks was utilizing 2 of the GPIO pins to power a siren (12mA max) and an LED (15mA max). I didn't think that affected anything as the other two backpacks did not use those outputs.
-Two of the analog inputs on the arduino have the potential to receive greater than 5V inputs. I have zender diodes in place to limit the total input voltage to the pin @5.1 volts.

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Tinkwithanr
 
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Re: LCD USB Serial Backpack Not Working

Post by Tinkwithanr »

Any other input? How delicate are these chips? Do I need to filter the input voltage somehow? I would have thought the Pro Mini would show issues too if it was a voltage issue from the environment.

What kind of warranty do these have? I'm willing to rework my power supply circuit but I don't want to keep having to buy a screen+backpack everytime a backpack dies. I've already got a lot of extra screens lol.

I was planning to do a production run of around 200 units once I finished my quality testing, but if I can't solve this I'm going to have to look elsewhere for a screen solution.

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adafruit_support_mike
 
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Re: LCD USB Serial Backpack Not Working

Post by adafruit_support_mike »

The LCD driver chip is fairly durable, but automotive environments throw a lot of noisy power around. The fact that it's happening after a power cycle leads me to think you're getting some kind of power spike.

Could you post a photo of your hardware and connections please? Maybe that will give us some clues. 800x600 images usually work best.

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Tinkwithanr
 
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Re: LCD USB Serial Backpack Not Working

Post by Tinkwithanr »

Sorry for the delay. Here is a picture of the board that holds the Mini Pro and all of the sensor connections. It also has the 5V, 1A regulator I've been using to run the Mini Pro and Backpack/lcd. The 12-14V power comes into the board at the bottom, goes through a diode and then to the regulator.

Image

The next picture is the back of the main board. The black residue is a non-conductive putty used for insulating high voltage industrial motors. I used it to just hold the board in it's box and make sure nothing contacted/shorted out the backside of the board. Most of it was removed before taking the picture.

Image

Here's the soldering on the lcd and backpack itself

Image


I also forgot to mention this before, but I built a 'test box' to run the units outside of a vehicle environment (pictured below). The test box using a standard brick 12V wall plug and few Pot dials to mimic the different sensors. One of the three backpacks I had died while being used with this setup, so I don't think it's a power spike from the vehicle.

Image


The main board connects to the car/test box through a standard 24pin atx connector. Here is the test box connected to the mainboard.

Image

I also took the time to hook up an oscilloscope to the 3 pin connector going to the backpack. The picture below shows the 'clean' 5V signal over a few power signals. Bascially I just plugged/unplugged the jack from the power brick. The top reference line is +5V and the bottom line is 0V. I did this for a few minutes and wasn't able to reproduce any kind of power spike.

Image

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Re: LCD USB Serial Backpack Not Working

Post by adafruit_support_mike »

The power switching looks pretty clean, but just to be sure:

- set the scope to capture a single event
- set the trigger to catch a rising edge
- set the threshold at about 5.1v
- crank the timebase down to about a microsecond

Then try another connect/disconnect cycle. If nothing triggers, take the threshold down to 3v and try again.

Any overshoot would happen pretty fast, and would be below the resolution of a 2.5s scan.

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Tinkwithanr
 
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Re: LCD USB Serial Backpack Not Working

Post by Tinkwithanr »

This first graph shows the response of the system when hooked up to the vehicle as it would be in the final installation. There does appear to be a small voltage spike, but it only reaches up to 5.02V max. I wouldn't have thought that would be enough to damage the chip.

Image


I also took a reading from the 'test box' setup just to compare the two. With this test I had to lower the trigger voltage to 4.8 before I would get a consistent trigger response. Anything higher than that didn't read every time. The final voltage does get up to around 4.95, but for some reason it wouldn't trigger the recording function.

Image

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Re: LCD USB Serial Backpack Not Working

Post by adafruit_support_mike »

Well that rules out the supply rails.. 20mV of overshoot is way too small to damage anything.

Your construction looks first-rate, so I wouldn't expect any trouble from that..

Check the voltage on the D+/D- pins. Those are limited to 3.3v by the USB spec, so it's possible that something might be happening there.

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