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Monthly Archives: February 2014

Investigating Portable DVD Player LCD Interface

Gutted DVD Player

I recently picked up this old portable DVD player marked “Doesn’t Work” for cheap at the local junk shop. My intent was to figure out the LCD interface and attempt to drive the display. This article is just the investigation. Once removed from the player, the LCD module and backlight is contained in a metal can, connected via a flat-flex to a small interface board, which conveniently contains the back-light driver as well. Its probably easier to just use the provided interface, so I examined the signals going into that. Luckily, the screen still worked perfectly, and I was able to power up the device outside of the body in order to get my scope on the pins. There were 24 pins in total, and helpfully, there where 23 labels on the rear silkscreen of the interface board. The below table shows those pins from top to bottom of the board (the side with the 4 pin connector at the top), along with the labels and my findings. I’m using an old 20MHz analog scope, so some of the measurements may not be precise.

Probe Setup

Also, be sure to set your probes to x10 for high speed measurements. More info here.

TFT_STH High pulse every 64uS, very short pulse. Based on the PCB label and speed, I’ll call this ‘Horizontal Strobe’.
TFT_STV High pulse every 17mS, very short pulse. ‘Vertical Strobe’. Note that this timing shows about 265 ish Horizontals per Vertical. Also this implies 60 FPS.
CKV 4uS High pulse every 64uS. This pulse edge is 12uS before STH. ‘Vertical Clock’.
OEV 4uS High pulse every 64uS. This pulse edge is 4uS before CKV. ‘… Vertical’
— —
OEH 4uS Low pulse every 64uS. The edge is 2uS after CKV. ‘?’
GND Ground
CPH1 .1uS Squarish Wave. About 10 MHz. As the fastest signal. I’m guessing this is the Pixel Clock. Not sure if the wave appearance is the fault of the scope, of if more is going on in there.
GND Ground
89P_VCOM 128uS Square Wave. Transitions in the middle of the CKV pulse. Seems to alternate high low every other line.
GND Ground
TFT_R Pixel data. Red. Couldn’t trigger on signal, but has patterns that align with pixel clock and CKV. Analog signal.
TFT_G Pixel data. Green. Couldn’t trigger on signal, but has patterns that align with pixel clock and CKV. Analog signal.
TFT_B Pixel data. Blue. Couldn’t trigger on signal, but has patterns that align with pixel clock and CKV. Analog signal.
GND Ground
— —
GND Ground
GND Ground
VCC +5V
BLVCC +5V. Must be for backlight.
GND GND
GND GND
TFT+5V +5V
+5VPV +5V
GND GND

That actually paints a pretty cloudy picture of whats going on. Mostly because I cannot find the specs for this screen, so I’m going to have to guess the resolution. The vertical strobe shows that around 265 lines are transmitted per vertical clock pulse. That sounds like a good vertical resolution, but at 17mS per vertical strobe, that’s about 60 FPS. So there must be some kind of interleaving of data somewhere. That makes sense because the 89P_VCOM line alternates high/low for every other line. Possibly some type of high byte/low byte scenario? I ran the screen while holding this pin low, and the image became washed out. So its a possibility. Since each horizontal strobe is 64uS, and the pixel clock is .1uS, this shows about 640 bits per RGB channel per line. Now, 640 sounds like a reasonable horizontal resolution. Originally this had me confused as I assumed the RGB pixel data signals were digital, when they were actually analog.

That’s about all the info I can gather for now. I won’t be able to tell if my assumptions are accurate until I hook it up to something. I’ll end with my scope readings for those playing along at home.

I was able to confirm that the RGB lines going into the panel are in fact analog. I attached a potentiometer between 5V and ground to form a simple voltage divider and attached the tap to the Red line. Turning the knob I was able to adjust the Red level of the image.

CKV signal.
CKV

CKV Compared to 89P_VCOM line
CKV 89P

CKV Compared to Pixel Data Line
CKV Pixel Data

Pixel Clock With Pixel Data
PixClock PixData

Adjusting the analog red input.
Analog Red Input

LiPo Charger Recovered from Portable DVD Player

Like most people, I love taking things apart. Usually I’m foolishly drawn to take things apart in order to reclaim parts for reuse later. However, it can be a chore to find reusable parts, especially in modern consumer electronics. I picked up a broken portable DVD player (GPX PD708B) from the Goodwill outlet store. They price hard goods at $.79 a pound, so usually it’a a cheap way to get stuff like this. Now, I had done this to remove the LCD and attempt to drive it, as a learning exercise for myself. Now, I hadn’t even looked that close at the unit until I brought it home. The first unexpected thing was that it contained a sizable 2000 mAh LiPo battery. That could definiately be re-purposed in a future experiment. As a nice supprise, I found that the charging circuit for the battery, was actually separate from the main board on its own little module. Awesome! Now I not only have a large LiPo battery, but a propery charger/control circuit for it.

LiPo Charger

It seems to be a complete unit with DC power input, battery power output, managed charging, battery protection, and an empty space to add a charge status LED. It appears to be run off an unmarked (at least I couldn’t see any markings) ATTiny micro. My only clue was the name on the silkscreen was “Lili-new-2Li-TINY13.” A little probing with my meter and scope found that the IC on the right of the board had 5V and ground in the right spots, pin 5 was outputting the “blinky” signal for the LED, and pin 6 was actually spitting out a 32 kHz PWM signal with about 30% duty cycle. See below for my brief examination of the board.

Labled Lipo Charger

Always nice to actually find something useful.

Project Frosty Mug, Part 2

Cup cooler #3

Build #3

In my continuing effort to build a working cooled cup holder, I’ve put together another unit. In this attempt, instead of using a plate and having the container cooled from the bottom I decided to attach it to the side, and have a small enclosure to attempt to insulate the beverage a little bit to help increase the cooling effect. Also, from my experimentation in part 1, I found that the cooling elements produce tons of heat, and so would need a quite large heat sink to keep things cool. Since these devices work by producing a certain temperature delta from one side to the other, keeping the hot side as cool as possible is key, and apparently very difficult. Cooling from the side allows for a large sink without holding the beverage up in the air. As you can see in the above picture, this build features a large Dell workstation CPU heat sink I scored off EBay for about $15. These are nice and feature a copper base fused with copper tubes that carry the heat into the aluminum fins. A salvaged fan forces some air through the fins.

The main design of this build features a printed cylindrical body with an opening on one side. Aluminum sheeting is cut and fit on the inside of the container to help transfer the cooling to all sides, and a piece of aluminum flat stock is used as the main contact with the cooling element and covers the opening. The cooling element used is a 12 volt, 16 amp version. Two large U brackets hold the assembly together and press the heat sink tight to the hot side of element. I’m using the same 10 amp, 12 volt power supply brick as the previous experiment.

Test Results

In this experiment I’ve powered on the element and placed a glass container of Diet Sun Drop, measured at about 38F to start, and let the unit run for approximately 30 minutes. The plate measured about 33 F inside the container while running, and the heat sink fins stabilized at around 100F. That’d a good step forward, as previous experiments seemed to just keep getting hotter. However, it did not manage to keep the soda cold. After the 30 minutes, with the ambient temperature around 70F, the soda measured about 45F, not a huge increase, but nowhere near our cooling goal.

Conclusions and Analysis

Reflecting on the experiment, I’ve already noticed several problems. One, I didn’t use a control. That is, I should have left another soda on the bench next to the experiment and measured its after temperature as well. This would give a measure of how much effect, if any, that the cooler had on the soda. Secondly, I was overloading my power supply. It measured about 145F after the experiment. What I didn’t measure was the voltage output of the supply to ensure the load wasn’t causing the output to sag.

In the next round, I will try a few improvements. My fan, while very quiet, could be a little faster to keep the heat sink temperature down, which should decrease the cold side temperature. I will use a higher current power supply to ensure the element is operating at full power and the supply can operate in a safe manner. I may try higher power cooling elements as well, and possibly experiment with stacking the elements to achieve colder temperatures.

This project is turning out to be more challenging than originally planned. However the prospect of keeping my soda cold with a high power home built contraption is enough to keep on trying. More to come…..