CDM102 Bed clock part 1

I’m personally obsessed with LEDs since when I was a kid, especially with LED display. I have a collection of vintage LED displays (and VFD) such as HPDL1414, HCMS 2915, SCDV5544/5542, VQC10, MN15439A, MN28016A. And now I’m adding CDM102 (and CDM101, coming soon) to the collection.

Back in 2020. I was browsing Taobao. And I came up with the never-before-seen LED display. CDM102. I was used as status indicator in 10Base-T switch. The link is here. (Off topic, I bought from this seller before. LTL-7100M back in 2020. And I bought it 5 more last month xD.)

There’s little secret in this picture, Can you spot it?

There’s some documentation out there of people using CDM102


Frankly speaking, I really want my hand on CDM102. The problem is that this thing is so rare. And the last listing on eBay is “Currently sold out”.

I gave up and forgot about it….. until last month.

This year, I bought several electronics component from Taobao with “Proxy” via the website called Yoycart. And no, This is not sponsor. Easy way to describe this web site is that. You ask the Proxy for the price of item you want (Difficult communication here). They will ask the store owner of that item that you want to buy. Then you can place an order. Also at the payment, you need to “Guess” the Item(s) weight. Since mine was just electronics components. I make sure that the weight that I type in never more than 100g. So I can have $3 shipping fee instead of $8.

And this is the Listing of the CDM102 on Yoycart. The product ID is just a copy from original Taobao listing.

I actually contacted the store owner who selling this LED module back in 2020. But back then I’m sure that Yoycart is scam or now and I can’t buy from Taobao directly. But now I know that they MIGHT not be a scam. Although, the Item price has some profit for them (Yoycart) added to the price. But Anyway. I got an item and here it is :

Up and running with STM8L and 250F supercap xD

I thought I will use the CDM102 with ESP8266 to do the Google calendar synced thingy. But I realized that It would be better to make a Bed clock out of this LED display.

Also, If you visited the Taobao link above and saw the Pic I took. I actually gave the store owner to put this up on they listing.

I quicky grab my sketch book to draw 5×3 fonts. And write a example code to light the display up with STM32. After I make sure that it’s working correctly. I moved to STM8L and start coding the Bed clock code. The code is now on the GitHub in my stm8l_sdcc_template repo.

After the Bed clock breadboard prototype is working. I then proceed to build the actual Bed clock. I also decided to use SMD rotary encoder as time setting navigation.

Here’s the part list that I use with this Bed clock project

  1. CDM102 LED display.
  2. STM8L151F3 (I have the Blkbox board, Will made one my own soon).
  3. SIQ-02FVS3 SMD encoder (Or any encoder you like).
  4. Small perf board.

As of time of writing this. The code is still in testing. As I will added more feature and fix bugs. For now lets enjoy pics that I took

Start with Soldering the CDM102, then the encoder
This is what the front looks like
On the back. Note that I already added 0.1uF caps to Encoder to fight with bounces.
The final result UwU

I yet to explore the CDM102. The op code set is quite similar to SCDV5542 and other 5×5 LED display from Siemens. I also saw that some people getting Green and Orange mixed in same “Group”.

For now I’m not digging deep into the CDM102. But I definitely will! So stay tune for the next part!


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