How to Build an OT-Hobbies D-I-Y Board
"Certum quod factum"
(one is only certain of what one builds)
- Giambatista Vico (1668-1744).
OT-Hobbies D-I-Y boards require fabrication. This may sound like work, but you end
up with a board customized for your specific application.
Probably the best way to build such a board is to follow the following procedure,
which entails building up and testing one section at a time, and then going
to the next section. It's just like coding software.
Add the parts for each section, only as needed for your application.
Pretty soon, you have exactly the board you needed from the start, and you may also
have a few parts left over to use on other projects too.
Refer to board schematics and build documents while proceeding.
- first, never ever plug in any chips until basic tests have been performed,
as described below.
- get out your
DMM (digital multimeter),
and set to the 20V DC volts scale.
If you don't have a DMM, go out to Harbor Freight, etc, and buy one right now.
An inexpensive $5-10 DMM will work fine; no need to spend $50.
- find a nice unregulated wallwart rated as 6-9 VDC at 500 mA or more, or a
7-9V regulated one.
It should have a 2.1 mm coaxial plug with center-pin positive.
Get the polarity straightened out "before" plugging in.
- wire up the power supply - voltage regulators and caps - and test board "buss"
voltages as shown on the schematic, before proceeding.
- for boards with a microcontroller chip, do steps 6 - 10.
- wire up the chip socket, crystal, crystal
caps, decoupling caps, Reset pin pullup resistor, and Reset switch.
Be sure to use a socket so you can fix a possible blown board later on, if needed.
Never solder a non-surface mount chip onto the board.
At this point, the board is almost ready for operation.
- IMPORTANT - with no microcontroller chip plugged in, test for 5V on the
socket VCC, AVCC, and Reset pins (refer to the proper ATmega chip datasheet or
- if an ATmega chip with a preloaded sketch (such as blink an Led) is available,
plug it in, power the board, connect the DMM to the "blinkie" pin, and the voltage
should jump between 0 and 5V. And you're in business.
Just don't plug the chip in backwards - people do it all the time.
- be sure to get the preceding working "before" proceeding.
Never let bugs accumulate - they're much easier to fix one at a time, rather
than 12 at a time. Same for software.
- almost totally operational now. Add the FTDI RS232 circuitry (header, cap, resistors)
per the schematic, and then program the microcontroller for real, using the Arduino
That finishes stage 1. Only about 20 parts installed, less than an hour of effort,
and the board is already working, and programmable. How easy was that.
- after this, the same idea is used to build up successive parts of the board.
Work in stages, wire up a section to be used in your particular application,
and test each as you go along.
- add the headers and series-Rs or voltage-dividers on the I/O pins.
How to Hack an Adjustable Voltage Regulator.
© OT-Hobbies, May 2013