Ahmed Obaidi

[ahmadobaidy]

Arduino with Eclipse and External Programmer

I have been tinkering with Arduino for a couple of weeks now. I’ve ended up creating my own PCB based on Arduino Mega and then I created another one based on Arduino Leonardo. To simplify the electronic circuit and to minimize the cost of the board, I didn’t include the USB programming circuit, and settle for ICSP only.

Of course, that meant I would need an external programmer to upload my code to the boards. So, I got Pocket AVR Programmer from Sparkfun. It worked nice and it was small and cheap.

Everything worked fine until I could no longer ignore the fact that Arduino IDE is peace of crap. It has no code completion, refactoring or error high lighting. The IDE might work just fine for small projects, but it just doesn’t scale!

I’ve turned to my old friend eclipse. I found a nice plugin for Arduino in the Market Place. I installed it, and bingo, I’ve got everything eclipse has to offer, and I got it for Arduino.

The only problem was that this plugin didn’t support external programmers. The work arounds I found didn’t work with the new versions. But after checking the correct avrdude command executed by Arduino IDE with the one executed by this plugin I’ve come with this hack. In the Arduino folder (the one used by the plugin), edit boards.txt. Modify the upload protocol for the board you are using from wiring to usbtiny.

#mega2560.upload.protocol=wiring mega2560.upload.protocol=usbtiny

You also had to go to the properties of my Arduino project in eclipse, and in the Arduino tab, set the COM Port to ‘usb’. This should convince avrdude to upload the code using USBtinyISP.

Happy hacking.

[ahmadobaidy]

Ardiuno and 4–20 mA Current Loop Sensors

The 4-20 mA current loop is a very robust sensor signaling standard. Current loops are ideal for data transmission because of their inherent insensitivity to electrical noise. In a 4-20 mA current loop, all the signaling current flows through all components; the same current flows even if the wire terminations are less than perfect. All the components in the loop drop voltage due to the signaling current flowing through them. The signaling current is not affected by these voltage drops as long as the power supply voltage is greater than the sum of the voltage drops around the loop at the maximum signaling current of 20 mA.

Recently, I came to a project where I needed to interface 4 current loop sensors to an Arduino based board.

To read a sensor I just need to complete the current loop using a resistor and then measure the voltage across that resistor. I wanted to isolate the ground of the sensors’ signals from each other and from the rest of board. So, I decided to use a differential analog-to-digital converter. Having no need for fast conversion and not wanting to sucrify too many pins, I decided to look for I2C IC. Luckily, I found ADS7830 from Texas Instruments. The ADS7830 is a single-supply, low-power, 8-bit data acquisition device that features a serial I2C interface and an 8-channel multiplexer. It could be used with 4 differential or 8 single-ended inputs. The circuit is very simple. The IC has an internal 2.5V reference, so I used 120 ohm resestor for sensing a maximum of 20 mA current.

The code to read the IC is quite simple too, once you figure out how to write the command byte (refer to the datasheet page 13).

cmd=(channel<<4) | 0x0C; //Internel Reference ON, Conversion ON And differencial

Wire.beginTransmission(HART_ADR); // default address 0x48, A0 and A1 set to GND

Wire.write(cmd);

Wire.endTransmission();

Wire.requestFrom(HART_ADR, 1);

sensor= Wire.read();

The 8-bit resolution is quite enough for my application, if you need a better resolution you can use the LTC®2309 8-channel, 12-bit ADC from Linear.