DSO nano - portable digital oscilloscope

I was really interested about it when Seeed Studio first announced the DSO nano on their blog, unfortunately I was not able to get one of the beta’s which they offered in a limited number at a lower price. The specs they released don’t advertise for too much power from this portable but it’s style and the fact that is portable together with the low price tag should compensate for the lack of power. And don’t get me wrong on the power issue, the 1 MHz bandwidth is still enough to cover your hobby needs. For me the only big disadvantage is the fact that it has only one channel, but it compensates with the ability of recording readings that you can later compare with the actual reading.

I would love to give you more details about this portable oscilloscope, but I have to wait until I can get my hands on the DSO nano. I’m currently waiting for Seeed to list it on their product page so i can place an order.

I recently ordered some samples from TI, which included the TMP275 digital sensor. The sensor has some nice features which I quote from it’s datasheet:

The TMP275 is a 0.5°C accurate, Two-Wire, serial output temperature sensor available in an MSOP-8 or an SO-8 package. The TMP275 is capable of reading temperatures with a resolution of 0.0625°C. The TMP275 is SMBus-compatible and allows up to eight devices on one bus. It is ideal for extended temperature measurement in a variety of communication, computer, consumer, environmental, industrial, and instrumentation applications. The TMP275 is specified for operation over a temperature range of −40°C to +125°C.

The easiest way to get the temperature out of the TMP275 seemed to be I2C. So I started by designing a board which has all the components needed: the sensor, an atmega8 brain, and some other components needed for the display and for powering the board. The display is a 4 digit 7 segment display from kingbright product code CA56-12GWA. As for the display part of the board, I used PNP transistors on the common anodes and resistors on the segments to limit the current draw on the atmega’s pins. The transistors are not current limited so the display will alaways light-up the same no matter how many segments are turned on.

TMP275 digital thermometer board

For the supply part of the board, I choose to make it portable and power it from a 9V battery, so I needed to use a voltage regulator. The choice was the good old 7805 because it’s cheap and easy to find.

I2C is a pretty common protocol so various libraries can be found on the web. I chose Peter Fleury’s I2C library because it was very well documented. The only external components needed by the TMP275 are a bypass capacitor between VCC and GND and two pull-up resistors required on SDA and SCL lines.

All the I2C stuff is handled by the library, so I only had to write a couple of lines of code to get the temperature out of the sensor:

 i2c_start_wait(sensor+I2C_WRITE);	// set device address and write mode
 i2c_write(0x0);			// write pointer register 00000000 to select temp register
 i2c_rep_start(sensor+I2C_READ);	//set device address and read mode
 temp_high=i2c_readAck();		// Read high byte of temperature
 temp_low=i2c_readNak();		// Read low byte of temperature

After reading the temperature from the sensor I had to display it on the 4 digit display. For that I had to write a display macro, which figures out the numbers and how to display them, basically I used software multiplexing. I even tested it on negative temperatures by placing the sensor in my fridge :). The readout was correct because I checked with another thermometer.

These new type of digital sensors are great, because you don’t have to worry about analog to digital conversion, all the  ADC is done inside the sensor. I mainly started working with this sensor because I want to incorporate a temperature reading function into a future project. Now that this part is done, is time to move onto the next one, ultrasonic range finder, which I’m guessing wont be as easy as the temperature reading.

I tried to comment every line of my code, but if you feel you don’t understand something, just post a comment and I’ll reply.

August 22nd, 2008

Sony DSC H9 review

Sony DSC H9 review

You’ve probably noticed the pictures from my last projects… they look pretty cool. That’s because i got a new camera, a Sony DSC H9. The macros are great, i can see the particles of dust on my circuit boards, the landscapes are great, i took some stuning pictures in my vacation in the mountains.

I’m not gonna go trough all of the aspects in this review, I’m just gonna tell you what impresses me about this camera. I payed for it at a local retail store about $520 complete with a 2 GB memory stick pro duo. The camera was nicely packed and accesorized. For example i got a cool remote control, that i can use to take pictures remotely. I also got a shoulder strap which you don’t get on most cameras.

The battery, is sony, as expected and it last actually more than they say it will. They guarantee that it will last you 300 photos, but i take aprox 600 photos with one charge.

If you plan on getting one, i suggest you take no less than 2 GB memory card. Because on 2 Gb it rarely gets full, and you’ll alaways have room for more pictures when you’re away from your computer and you can’t download them.

Another good thing about the camera, it’s the 15x zoom complete with image stabilization, which helps you get more acurrate details into your pictures when shooting at a distance.

The camera also has other nice functions like many shooting resolutions, the i prefere beeing the widescreen mode. In my opinion this is the best choice in digital camera before moving into the SLR category.

I hear that digital photo frames are they way to show your pictures arround the house these days, maybe one from Sony will work ok together with my H9.

July 27th, 2008

FPGA Digital Oscilloscope

FPGA Digital Oscilloscope

The guys from fpga4fun have this interesting recipe for a simple digital oscilloscope which is made with the following parts:

  • 1 x Pluto FPGA board, with TXDI and cable (item#1121, $39.95)
  • 1 x Flash acquisition board (item#1200, $29.95)
  • 1 x BNC (item#1250, $4.95)
  • 1 x Nylon standoffs (item#1270, $0.95)
  • 1 x Male/female connectors 28 (item#1275, $2.95)

That’s about $78.75 so you can also call it a cheap oscilloscope because all commercial oscilloscopes are priced higher than $70.

FPGA Digital Oscilloscope: [Link]

DS1803 Digital Potentiometer

They’re “digital” because you can control the resistance over its range programmatically, by sending it commands over a 2-Wire (I2C/TWI) serial interface. So, that means that you can hook it up to some microcontroller, like the Arduino, and adjust the resistance in a little program. The DS1803-010, means it has a range of 0-10K Ohms.

DS1803 Digital Potentiometer: [Link]



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