Electronics > Projects, Designs, and Technical Stuff

Easy DIY 5.5 Digit DVM + Volt Ref./Cal. (LTC2400+LTC6655 / SPI uC / Arduino)

(1/51) > >>

quantumvolt:
After I saw (the late) Jim Williams video on the Linear Technology Voltage reference LTC6655, I bought the 2.5 V version (a bit more than USD 10). In addition to be a 'nice to have' very low noise modern reference, it came to me that I have seen a lot of DIY precision DMM designs out there - but few of them have made it to actually measure anything.

So I decided to make a 6 1/2 voltmeter and bought the cheap LTC 2400 ADC (a tad more than 10 dollars). After reading datasheets and looking around the web, I realized that you can have a breadboard built meter running in less than an hour.

The pictures show a working prototype on top of an Arduino. If you are hip/cool/serious or in any other way too good for Arduino, you can hook the meter to any microcontroller that has 3-5.5 V DC supply and SPI. But if you need protection against hundred of volts or ruggedness that survives falls from 6 feet height you'll be better off looking elsewhere ...

I like these LT devices better and better - they are quality, cheap, simple to connect, rugged and well documented. Combined with the low noise op amp LT1012 as optional front end (buffer/amplifier/ADC-protector), this gadget (which even uncalibrated will give accuracy better than 0.025% / around 4.5 digits) also fills a real need for me: I can measure voltages with more than 3 1/2 digit resolution even when my Agilent 34401A is locked up doing long time data acquisition .

I will use this thread to post all information I have found about these devices and uses of them  :-DMM :-+

BravoV:
Thanks for sharing, really interested on how you deal with the analog front end for the LTC2400, please post the schematic.

I have few for this 24 bit adc gathering dust for years.  :-[

quantumvolt:
Documentation from Linear Technology:


LTC6655

Jim Willams: 775 Nanovolt Noise Measurement for a Low Noise Voltage Reference
http://video.linear.com/p4187-7

Product page
http://www.linear.com/product/LTC6655

Datasheet
http://cds.linear.com/docs/en/datasheet/6655fc.pdf

Product Video
http://video.linear.com/p4187-36

AN124: 775 Nanovolt Noise Measurement for A Low Noise Voltage Reference
http://cds.linear.com/docs/en/application-note/an124f.pdf


LTC2400

Product page
http://www.linear.com/product/LTC2400

Datasheet
http://cds.linear.com/docs/en/datasheet/2400fa.pdf

Demo board
http://www.linear.com/demo/DC573A

AN78 - A Collection of Differential to Single-Ended Signal Conditioning Circuits for Use with the LTC2400, a 24-Bit No Latency Delta Sigma ADC ...
http://cds.linear.com/docs/en/application-note/an78fs.pdf

AN80 - How to Use the Worlds Smallest 24-Bit No Latency Delta-Sigma ADC to its Fullest Potential
http://cds.linear.com/docs/en/application-note/an80.pdf

AN86: A Standards Lab Grade 20-Bit DAC with 0.1ppm/ °C Drift
http://cds.linear.com/docs/en/application-note/an86f.pdf

Design Solutions 11 - Testing Linearity of the LTC2400 24-Bit No Latency Delta SigmaTM A/D Converter Help from the Nineteenth Century
http://cds.linear.com/docs/en/design-note/dsol11.pdf


LT1012

Product page
http://www.linear.com/product/LT1012

Datasheet
http://cds.linear.com/docs/en/datasheet/1012afbs.pdf

quantumvolt:

--- Quote from: BravoV on September 23, 2013, 02:19:52 am ---Thanks for sharing, really interested on how you deal with the analog front end for the LTC2400, please post the schematic.

I have few for this 24 bit adc gathering dust for years.  :-[

--- End quote ---

I don't have a schematic. These bits are like LEGO - connect and play  >:D. But you will find a schematic at page 14 in the LT1012 datasheet linked over. (EDIT: Page 15. Also - you don't need +- 15 V as in the circuit diagram. Look at page 14 and page 1 and you will see that you can run single supply 3 V or more and symmetric minimum supply +- 1.2 V. Nice for batteries. If you want to include zero measurements you can use center tapped AA cells or use a charge pump inverter with the 9 V battery.)

Schematics, gerber and drilling is what I hope to get help for here  :-DD. I am too old for Eagle (my first programming was FORTRAN on VAC punch cards early 1970's). If a Shenzen PCB can be made these bits seem to be perfect for a low risk IGG project. Who knows? May be I'll do it.

quantumvolt:

Navigation

[0] Message Index

[#] Next page