Building the M328 component tester (1)

Having being inspired by one of Peter VK3YE recent video's, it was time to purchase a couple of kits and dust the soldering iron off the shelf and get down to building one:

This could prove to be a very useful piece of component test kit, for the constructor and repair bench, including the novice. It does, R, L, C  including ESR, Diodes and Transistors, giving the pin configuration detail of the Semiconductor device undertest as well as the useful gain figures. 

It is basically a copy of the Karl-Heinz Kubbeler design, centred around a programmable ATMEGA328 microcontroller which is very well documented. The kit took about 2 weeks to arrive from China, which contains a well made PCB, display module and all the components, including the blown main chip all for around £8.00 ($12 US). It comes with no instructions on how to put it together, but a Chinese manual is downloadable from the purchase site, which I will make a link available at the bottom of this Blog. Infact, really you don't need the manual for construction, as the component values are printed on the PCB, it just helps a little to get one or two things installed the right way around like the switch, and the circuit diagram can be useful for component reference and maybe fault finding later? Of course the Chinese manual is written in Chinglish, we are refered to welding not soldering! I don't think my old arc welder would prove very suitable for this project somehow? Hi!

I emptied all the components out of their anti-static packet into an empty biscuit tin, so I didn't lose any of them. I was away, it took around 2 hours of soldering, and sorting out the correct values, a DMM can help with the resistors values, as I found an orange band can look like a red, so its best to measure them to avoid confusion and getting one soldered in the wrong position. Transistors are marked to board values, and the marking of the outline makes sure you cannot put the devices in the wrong way around.

At this stage it is time to check the board over for shorts, man made solder links etc, and snip off component ends. All looked ok, time to connect the 9V battery, before inserting the main ATMEGA IC, at this point a DMM is required to check for regulated 5V at the IC socket pins 7 & 22, all confirmed correct and the regulator was doing its job!  
 
All in all it was quite a relaxing project to put together, I didn't find anything too difficult, although a bit of care is needed aligning up the pins of the main chip before pushing firmly home into its socket.

 



There is not much work to do with the display board as most of this is already constructed, just a strip of header pins that carefully require soldering in across the top of its PCB. This then mates up with the socket strip on the main board when it is pushed home and bolted together.




All looked good time to switch on! If it fires up correctly one push of the On button should turn on the display. In my case it did, and didn't? When I released the Push To Make switch, it went out ? Some folk have had problems putting the switch in the wrong way around, I knew I hadn't done this and a quick check confirmed the switch had been inserted correctly, time to investigate further? The clue was the LED under the display board wasn't on, a quick check with the DMM around the circuit in this area confirmed my thoughts, I had put the LED in the wrong way, huh! Oh dear! I had to pull it all apart, split the two boards desolder and turn the LED around, and then put it all back together.

Great it then fired up correctly, and held in its On state after pushing and releasing the button, a quick adjustment of the contrast pot to get the display correct and all was looking well, time to calibrate..

To be continued in part 2.

References:

This is where I purchased the kit from, although they are available from ebay too:

http://www.banggood.com/DIY-Meter-Tester-Kit-For-Capacitance-ESR-Inductance-Resistor-NPN-PNP-p-929603.html  

Construction manual:

https://www.dropbox.com/s/zpjwo3vfv9yfr5b/SKU136841%20M8install.pdf


Design manual helps with Calibration and other stuff:

www.mikrocontroller.net/attachment/143813/TTester_096k.pdf

Newer version of manual:

www.mikrocontroller.net/attachment/164956/ttester_eng104k.pdf