Teunis van Beelen
Electronics engineer

12 channel ADC-box with reinforced electrical isolation

This is an open-source ADC-box project. It includes the schematic, the boardlayout,
the Gerber- and Excellonfiles, the software used in the microcontroller and the aquisition software for the pc.
No SMD/SMT components are used in this design. Licences used in this project are GPLv2 and Creative Commons Share Alike.
I also designed a 12 channel Fullband EEG-amplifier that fits in the same housing.

Warning: This is an old project and it is not maintained. I have no time to support this project.
Some components are obsolete. It definitely should be modernized, the serial port should be
replaced with an USB-port (FT232), the optocouplers could be replaced with digital isolators,
use SMD components instead of THT, etc.
Last but not least, it lacks IEC60601 certification! So, do not try to build this project.
The reason I leave it here is only for educational purposes.




tip: To get access to the serial port on Linux, you need to be a member of the group "dialout".


Report any errors, mistakes, omissions to teuniz@gmail.com

Serial port issues

The ADC-box produces a constant dataflow of 9220 bytes per second. The hardware FIFO buffer of a normal serial port
has a size of 16 bytes which is not sufficient. In order to avoid data-loss, you need a serial port with a FIFO
buffer size of 128 bytes. For example the Brainboxes UC-246 or the SPEED1LE (I only tested the UC-246).
Do not forget to adjust the RX interrupt trigger level to 15% (19 bytes) or you wil get sync errors.
Unfortunately, the manufacturers do not provide Linux drivers.
For technical details about how to setup the UC-246 serial PCI-card on Linux, read this.


Sunix sells a PCI serial-card which is plug and play on Linux, so you don't need to install any drivers.
Modelnumber is SER4037A.
I tested this serial card in a new pc (Intel Core 2 Duo) with openSuse 11.2 and it works perfect, no sync-errors anymore.
p.s.: Since openSuse 11.2, you need to be a member of the group "dialout" in order to get access to the serial ports.

DC/DC-converter issue

The output voltage of DC/DC-converter IC2 (TMA1-0505S) is not regulated. It's outputvoltage can be more than the maximum voltage allowed
to the ADC-chips. To prevent possible damage, I added R17 (68 Ohm 0.5 Watt) as a quick and easy solution. It sinks some current and thus
lowers the outputvoltage. After adding a suitable pre-amplifier which consumes some current, you can increase the value of R17 or remove it .

External links

Software used for this project


Recommended reading