Tuesday, August 13, 2013

The modified 3208Clock Part 1 the beginning

I stumbled upon this lattice clock while I was surfing through the products of one of this Chinese Internet sellers with worldwide free shipping. I thought "OK, 12$ (~9,0 EUR) what can I loose?" So I've ordered one of this devices.

I have stolen this Picture from www.FastTech.com

After only four weeks the package has arrived. My first thought was to quickly unwrap it and connect it to power to see what it is doing...

It took me $12.30 and a lot of patience (waiting for delivery) to learn that this device can not be powered directly by 12V DC. After the magic smoke has disappeared and I have turned the PCB I have seen that this device is labeled with DC 5V

From this setback, I did not let me discourage and I ordered a new unit. During the delivery time for the new device I had some time to do some reverse engineering. So I unmounted all the parts which hide the direct view to the PCB.

The contents of the 3208Clock

This device consists of an ATmega8L which is the brain of the Clock and a Holtec HT1632C Display controller paired with four 8x8 LED segments.

Optional components

During my investigation I have discovered that the PCB was in general developed in a very clever way. The following parts can be retrofitted to the board.
  • Mini USB port
  • TSOP infrared receiver
  • DS18x20 1-Wire temperature sensor / LM35 temperature sensor
  • Bi-color LED (color changing by reversing polarity)
  • 6-Pin ICSP header to reprogram the ATmega8L
  • Buzzer/Speaker (can not be mounted if ICSP header is mounted)
  • On the backside is a place to mount a RTC IC and a coin cell battery to power the clock IC if the main power is not connected.
But due to the Problem that the ATmega8L has only 8KB of program space I'm not sure if all of the above components can be implemented into the software.

PCB Overview

The most interesting part seems to be the right part of the front side. Here are a lot of footprints of the unpopulated optional parts which can be used to interact with the real world.

I have prepared a picture which shows which pins of the ATmega8L are connected to the footprints. The numbers are the Arduino pin numbers. I was to lazy to also write the original port pin numbers like "PB3" to the Picture. But here you can see a very good pinout diagram made by Pighixxx. I know its for a ATmega168 but the Pinout is more or less compatible.

Here is a picture of the backside of the PCB. We see here that three ICs can be mounted to the board. From left to right we have at first the footprint for the ATmega8L with its TQFP32 package. The next ones are the footprint for a battery and a SO16 IC where a RTC can be mounted.
The last one is the Footprint 52 pin QFP footprint for the Holtec HT1632C driver IC for the 8x8 LED displays.

I also have made a picture with some additional descriptions for some pins. During my reverse engineering I also painted some pads red to make it easier for me to track the +5V line. Also take a look at the top left of the picture there is a very important information written which I have ignored at my first try.

My actual setup

The only parts from the optional components which I have installed are the ICSP header for programming the device and a bi-color LED which was laying around for debugging purposes.

With the Setup in the picture above I'm now able to send a zero terminated string to the device over Bluetooth which will then scroll through the display. Here is a short video which I have made.

The next steps

In the next posts I will show a more insight view about the single steps which I have made to get this device up and running with the Arduino IDE and a couple of libraries. I also want to upload a well commented version the code to GitHub so that everyone can get started with playing around with this cheap and versatile device.

I'm not sure which topic the next posts will have but they will be more or less related to the 3208Clock device. It is also possible to post requests for additional informations of specific parts of this device or the procedure of hacking it to the comments.