Electronics Kit Review: 4 Digit Clock

March 2016 ยท 3 minute read

Some time ago I stumbled on a site called Banggood. I was looking for some new electronics kits, harder than the lovely Velleman kits and I found a great LED clock kit for ten bucks – shipped!

Quality control can be awful sometimes when buying directly from mainland China, but everything worked well. The most trying thing were the directions. It’s a good thing electronics schematics are a universal language.

Let’s unpack the kit! (And look at my lovely workstation!)

Kit unboxed.

What do we have here? A hodgepodge of electronics, a lovely board, and a plexiglass case. Let’s dive deeper.

Board layout.

Interesting. Looks like a fun amount of soldering involved. And some chips… Hmm, what could they be?

Just the chips.

In case it isn’t clear, you’re looking at a DS1302 Trickle-Charge Timekeeping Chip and an STC15F204EA single-chip microcontroller.

Now the timekeeping chip doesn’t interest me much. But the microcontroller, hmmm. The clock tells the current temperature, but only in Celsius. Still on imperial in the states, I’d love to see that in Fahrenheit. And since this supports ISP like the ATmega series found in the Arduino, there’s lots of room for improvements in the software at a later date.

Partially completed board.

This is a very thoughtfully laid out little board. The biggest things to be aware of are:

  1. Make sure that you install the shorter components first. If you install the buzzer, battery mounts, etc. you will have a hard time with the hand gymnastics required to install the resistors and capacitors.
  2. The kit includes a thermistor and a fast switching diode that appear nearly identical to the naked eye. Don’t confuse the two or you’ll have a bad time.
  3. Buy a good magnifying glass or magnifying third hand. See previous.
Packaged case.

The case is paper covered plexiglass, just peel the paper and then it goes together with an interesting screw / nut mechanism. It looks slick. You can buy this kit without the case, but I wouldn’t. The case option adds around a dollar to the cost and it looks slick.

Rear of the completed clock.

All done! Looking at the rear you can see the adjustment buttons sticking out, you’ll have to spend a minute understanding how to set it, or you could try to decipher the directions, but the buttons well and have a good feel. The clock plugs into USB for power with a battery backup so it keeps the time even when unplugged. The little doohickey sticking out of the top is the thermistor so it can give you the ambient temperature.

Front of the completed clock.

As you can see this thing can get bright! It has a light sensitive resistor so it won’t blind you at night, but is still perfectly readable in full sunlight.

Its display cycles to show the temperature for three seconds after every 30 seconds.

Closing Thoughts

This clock does have some limitations:

  1. It displays time only in 24H mode.
  2. It displays the temperature only in Celsius.
  3. Periodically it will display a single number, 1-7 corresponding to the present day of the week. This seems unnecessary.

Unfortunately they don’t provide the source code to edit the program, but… open source to the rescue! Someone on GitHub has started work on a replacement firmware that allows 12 hour mode on the clock and is working towards other features. Maybe time to jump in and add Fahrenheit temperatures.

Overall, a great build, a fun product and I love it sitting on my desk.

Have fun soldering!