Archive for July, 2007

Inclinometer / accelerometer module

Monday, July 16th, 2007

Accelerometer module based on a VTI Technologies SCA3000 series 3-axis accelerometer. Mainly intended for inclinometer purposes but can be used for other accelerometer needs also. RS-232 and CAN interfaces and wide input voltage support. Accelerometer used in this module has +-2G range and also has a built in temperature sensor that can be used for calibration and temperature compensation.


It will be interesting to see how well this behaves, especially in environments with lots of vibration. Maybe a simple running average would work for filtering or then maybe FIR or IIR filters might offer some advantages.

There were couple bugs with this first PCB revision as it was the first time I have used the STR7 controller so I had connected the accelerometer chip select to the slave select pin of the STR7 just like in the first prototype tested with an AT91SAM7S evaluation board. But unlike AT91SAM7S it’s not possible to use that pin as the chip select in master mode but instead it has to be tied high for master mode operation with STR7. But nothing that little cutting of traces and soldering couldn’t fix.

Switching regulators

Monday, July 16th, 2007

Some general purpose switching regulators that are often needed when prototyping systems with battery power for example. Input voltages from 4V to 35V are supported and the output can be configured from 1.2V to 35V. There is also a place for a transient voltage suppressor at the input.

A small 1A buck regulator with optional input capacitor:

buck_regulator_1a.jpg buck_regulator_1a_with_cap.jpg

PCB waiting for a higher current version:


Buck-boost regulator:

buck_boost_regulator.jpg buck_boost_regulator_with_cap.jpg

Joystick interface + joystick

Sunday, July 15th, 2007

Joystick interface module in testing with a Apem 9000 series joystick and spitting out joystick position updates to CAN bus.


Looking at the output values they don’t seem to jump up and down more than 1 LSB so with a 12 bit ADC that gives a nice resolution for joystick use. So there probably won’t be need for much filtering except to catch some random glitches there might be.


Sunday, July 15th, 2007

Finally got a PCB made for a USB JTAG adapter using FT2232 chip. This has been on the todo list for some years now.


This is a lite version without additional buffers so it should work with target voltages from about 2.8V to 5V. There is also a second PCB version with buffers that should be capable of supporting target voltages from 1.65V to 5V.

JTAG interface like this can be used with OpenOCD for example.

Joystick interface

Friday, July 13th, 2007

And to complement the hydraulic valve driver board here we also have a joystick interface board.


A lot of it is the same as in the valve driver board like RS-232 and CAN interfaces, just the analog section has been changed for accepting input from joysticks and scaling the input signal to be suitable for the AD converter of the STR7 microcontroller. This board supports 4 analog input channels for the joystick axes and 12 digital channels for switches. There are also additional 8 general purpose IO pins in a separate header. These 8 IO pins can be also configured as two separate hardware SPI channels.

Bluetooth board

Tuesday, July 10th, 2007

Adding Bluetooth connectivity.

Bluetooth modules


Board built for experimenting with the above modules. Breaking out the serial interface and RS-232 level conversion + other interfaces.


Ratiometric valve controller

Monday, July 9th, 2007

Another device in development is a controller board intended mainly for generating the control signal for PVG32 hydraulic valves.


The controller supports both 12V and 24V systems and it has RS-232 and CAN interfaces for communication needs. There are 4 outputs so one module is capable of driving 4 valve sections.

In this module the ratiometric output signals are generated with digital potentiometers. Could compare if there is any difference to PWM generated PVG32 control signal.

The microcontroller used is STR712 from STMicroelectronics so there should be enough processing power for many things…

Also on board is a header with 13 I/O signals and 3.3V + 5V power supplies for additional hardware.