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Old Oct 02, 2008, 07:17 AM
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plane_spotter's Avatar
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Bruce Abbott's Wattmeter Project

Hi all, has anyone built Bruce Abbott's Wattmeter project. Have 95% of the parts so would like to give it a go. There is little in way of documentation so would like to hear from anyone who has had success. Would try Bruce direct but he has no email contact, and not sure if he still reads the threads here.

http://homepages.paradise.net.nz/bha...wattmeter.html

Cheers

Ash
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Old Oct 02, 2008, 11:04 AM
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Green Bay, WI
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Have a look at mine. I am updating it now with more features.

http://www.rcgroups.com/forums/showt...motor+analyzer
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Old Oct 03, 2008, 06:46 AM
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Hastings, New Zealand
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So far nobody has admitted to building my wattmeter, though a few people have asked questions about it. Please have a go - I'll be here if you need help.

Quote:
Originally Posted by plane_spotter
not sure if he still reads the threads here.
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Old Oct 06, 2008, 06:42 AM
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Thankyou both, will try Bruce's first then the other.

regards

Ash
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Old Feb 02, 2009, 09:13 AM
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Hi Bruce and all,

I want to build this wattmeter badly.

Questions:

- Got a PIC 16F876A on hand. Can I program the hex code of 16F870 to it and be still working? Google search said it's OK but like to reconfirm.

- Mylar 100n caps OK? Or Ceramic?

- How do you build the 0.001 Ohm shunt for such a small size?

- How do you calibrate using R13 and R14?

- I made a tachmeter using infrared emitter and receiver. Is it doable to route the signal to the "rpm input" of the PIC?

- How do you use S1, S2, and S3? Which should be placed on the front panel next to the LCD display and which inside the box?

- Parts list available?

- How accurate can I expect from it?

Thanks Bruce for your sharing. I've done a precision PIC based LC meter and another frequency counter with success. I really wish to hit it again with your wattmeter project.

Best wishes from Taiwan.
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Old Feb 03, 2009, 07:17 AM
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Hastings, New Zealand
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- Got a PIC 16F876A on hand. Can I program the hex code of 16F870 to it and be still working? Google search said it's OK but like to reconfirm.

The register addresses seem to be the same, so I think it would work. However, in case there is some difference, I have compiled a 16F876 version for you

- Mylar 100n caps OK? Or Ceramic?

I used ceramic caps, but mylar should be OK.

- How do you build the 0.001 Ohm shunt for such a small size?

Crude way:- Length of thick copper wire.
Better:- Precision shunt. If you can't get a 0.001 Ohm shunt then parallel several higher values (I used 3 x 0.003 Ohms).

- How do you calibrate using R13 and R14?

Measure input Volts with a multimeter, and adjust R13 to get the same reading on the Wattmeter. Connect a load resistor to the output, in series with the multimeter (set to 20A scale) and measure Amps. Adjust R14 to get the same reading on the Wattmeter.

- I made a tachmeter using infrared emitter and receiver. Is it doable to route the signal to the "rpm input" of the PIC?

Yes. The rpm input just needs a logic level pulse stream with one pulse per blade pass.

- How do you use S1, S2, and S3? Which should be placed on the front panel next to the LCD display and which inside the box?

S1: Momentary push-button. Press to change number of blades.
S2: Toggle On/Off. ON to hold readings, OFF for continuous update.
S3: Momentary push-button. Press to change display page.

- Parts list available?

No, sorry!

- How accurate can I expect from it?

Volts and Amps have 0.01 resolution, but may change by +-1 count due to noise, and there is also some non-linearity. For best accuracy you should calibrate with a voltage and current close to what you expect to measure (eg. 10V, 20A). Obviously it cannot be more accurate than the standard that you calibrate it from. I have 3 good multimeters and a Watts Up Meter, and none of them read the same!
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Old Feb 03, 2009, 08:10 AM
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For a good precision current sensing shut I have used the Isotek ones:
http://www.isotekcorp.com/productDis...ID=1&SubCatID=
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Old Feb 03, 2009, 07:21 PM
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Now we are cooking! Bruce and jh2rc97, Thanks a lot.

It's gonna take a few days for parts collecting and breadboarding. Will get back to you then either with success or be warned... more questions.

Happy flying.
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Old Feb 04, 2009, 06:44 AM
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Hi,
I built Bruce's Wattmeter just a few weeks ago. I used the PCB layout and the components, presented by Bruce.
I used the PIC 16F88. As a shunt I used three 0.003 ohm resistors in parallell.
I had to increase R5 a little, since the R14 range wasn't enough.
I have not tried the RPM input yet, but I will.

Everything worked fine. Thanks for a nice design!

/Pete
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Old Feb 04, 2009, 11:04 AM
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pete,

Any suggestion for R5 value? Thanks.
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Old Feb 05, 2009, 11:49 AM
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I had to use 180k. This will depend on the actual value of your currect shunt (R15).
You will have to test your set-up. If you are out-side the range of the pot (R14), you will have to change R5 until you are in range and can adjust the current setting exactly.

/Pete
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Old Feb 06, 2009, 03:24 AM
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Bruce Abbott's Avatar
Hastings, New Zealand
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Quote:
Originally Posted by ElectoPete
I had to use 180k.
That doesn't sound right. I'll just check my code to make sure that the external 2.5V reference is properly selected on the 16F88...

.

.

.

Oops!

Must remember that all symbols are case-sensitive, ie. '__16f88' is NOT the same as '__16F88'


Updated HEX file attached (please remove '.txt' extension before use).
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Old Feb 06, 2009, 01:23 PM
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Bruce,
I tested the new hex-file, but there was no change.
(The reference voltage was probably OK from the beginning - the voltage reading has been correct all the time)
My amp reading is correct as long as I use R5 = 180K.

I also tested the RPM input - with an old optical sensor from my Graupner MC20 Tx.
It seems to work - at least in-house with 50Hz lights it shows 3000 rpm.
I was a little concerned since the Wattmeter only utputs 3.3 volts - but it seems to work OK. I will test outside in daylight later.

/Pete
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Old Feb 07, 2009, 08:15 PM
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Hi Bruce and all,

While waiting for LM2936-3.3 and TL431 to be delivered, I breadboarded only the 16F876A (programmed with your tailored hex code) and LCD display circuitry using +5V supply. OSC1 and OSC2(pin 9 and 10 on 876A respectively) were also connected according to the schematics. What I saw was upper 16 all black out and lower 16 all blank. It seems that LCD routine was not running and LCD was not initialized. Does it sound normal to you?

Did some internet reading and realized there is the infamous issue with pin 24, the RB3/PGM of 16F876A.

Used caution I programmed the 876A hex code from the following:

http://www.voti.nl/blink/index_1.html

It worked and the LED was blinking.

I then again programmed the RTC876.HEX from the following:

http://pagesperso-orange.fr/fabrice....TC/RTC_I2C.htm

It also worked with only the 16F876A, the oscillator, and LCD display connected. I was able to read the message "Fabrice Sincere" on the display.

Note that the circuitry uses the infamous RB3/PGM driving the RS Register Select to the LCD display and it is working alright.

Back to our project, I programmed the 876A back to your hex and tested the LCD initialization. Still no go.

I will route the circuitry all over again when I get the rest parts.

Your advices are greatly appreciated if you see something wrong of what I had gone so far.

Thanks again for your sharing.

Daniel
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Old Feb 07, 2009, 08:39 PM
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Quote:
Originally Posted by ElectoPete
Bruce,
I tested the new hex-file, but there was no change.
(The reference voltage was probably OK from the beginning - the voltage reading has been correct all the time)
My amp reading is correct as long as I use R5 = 180K.
...
/Pete
Pete,

How the voltage accross the shunt resistor is sampled will affect the gain needed by R5 and R14 et al. R7 and Source 0V leads should be soldered as close to R15 (the shunt) as possible.

Daniel
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