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.


Properties



Downloads



Notes


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


Feedback


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.

Update:

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


Datasheets


Recommended reading