tengu clone on pcb

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Tengu clone on PCB

May 3rd, 2008 · 40 Comments · PCB, avr, led, sound

This is a new version of my Tengu clone. This time on a printed circuit board (PCB). I have them

produced by Olimex and I am very pleased with the quality. The PCB worked on the first try and

has some minor issues only.

MATERI

ALS

Tengu PCB



E verlight 8*5 LED dot matrix

A Tmega48, 4kB Flash R AM, 512 bytes R AM

4 MHz crystal

LM386 Op- A mp

28 pin header

8 pin header

2 * 22pF capacitors

3 * 100nF capacitors

10k potentiometer

100k potentiometer

100k resistor

5 * 1k resistors

2 * 7 pin header sockets

2 pin headers for power supply and microphone (optional)

Electret microphone (not on the picture)

Note, that the electret microphone has a polarity. On the PCB the inner pin is the positive one. If

you connect it the wrong way, it is heating up really quick.

The microphone that I used here has an impedance of 2k. You may have to experiement a bit

with different microphones.

The capacitor C2 is used to control the amplification of the LM386. I used 0.1uF but you can use

up to 10uF to get a stronger amplification. Here is the amplifier circuit that I used.

PCB DESIGN ISSUES



A s this is my first design, there are a couple of things that I would redesign.

A s I tried to insert the pin header sockets, I realized that the drill holes were a bit too narrow.

You have to use a bit of strength to insert the headers, but it works.

A ll solder pads used for resistors and capacitors are a bit too small. It was a bit difficult to solder

them. I would make them a larger next time.

I think I should use a bit less of the silk layer. Some solder pads are covered with silk. Most of

the time that does not hurt as it is on the top side. But there are pins that you may wont to solder

on the top side, e.g. the power connector.

IMPROVEMENTS

The component count could be reduced if I had dropped crystal. For the animation of the LED

matrix the internal oscillator would be sufficient. On the other hand, with a suited crystal, this

circuit could be modified to display the time.

I would add an ISP (in system programming) header for easier programming. Now you have to

flip off the display, take out the controller, program it, re-insert it and put the display back in

place. Not a fast turn around if you want to modify the firmware.



W hat would you think of an A rduino version of this circuit? The controller could be replaced

with an A rduino compatible A Tmega168. Or maybe as an A rduino shield?

CONCLUSION

It is great to see your first produced PCB. E ven better if it works on the first try. Maybe I can

even build a kit out of it with the next revision of the board.

tengu clone on pcb

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