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1S Wattmeter

Homebuild electronics project

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Chris Bott - Moderator23/05/2020 11:35:40
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Dennis, thanks for pointing that out, the 1uF tant is indeed C1 and not C2. I'll correct the bill of materials. -ve end goes to ground which is a thicker PB track.

Dennis Mulhair24/05/2020 10:55:49
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Chris, Is the software in the Dropbox contain the latest updates?

Thanks.

Dennis

Chris Bott - Moderator24/05/2020 13:08:05
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Hi Dennis yes the latest version is V0.3.

Here's all the links etc in one place.

Sketch OLEDPwrMtr V0.4.ino (V0.4 includes the change to the line three posts down).

.stl file for PP3 Battery Box

.stl file for Middle section

.stl file for Bezel/Front is from the bottom of this page on the Bitsbox website

Bill of materials

bitsboxbom.jpg

Edited By Chris Bott - Moderator on 02/06/2020 21:31:01

Dennis Mulhair24/05/2020 19:29:40
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Hi Chris, The board is built and the Minipro 328 has accepted the sketch so its ready for final testing. Can you please run through how I setup the calibration of the unit using the two trims.

Thanks Dennis

Chris Bott - Moderator24/05/2020 19:47:27
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Hi Dennis. That's sounding very positive.

All I do, to be honest, is:-

  1. Adjust volts - Apply a voltage to be measured, I tend to use a 1S battery for this because that's the typical use case, and check this voltage at the same time with a multimeter. Adjust Trim V until the readings match. Then if you like, try at other voltages.
  2. Adjust amps. This is a little more tricky as you need a source and a load so that current passes through the unit. I use a bench power supply that has a current limiting adjustment and a car headlamp bulb. I put a multimeter in series with the bulb, on it's 10A range. Then I adjust the current to something like 2A on the multumeter and adjust Trim A to make the wattmeter read the same. I then try at around 1A just as a check. Without the adjustable supply you could use a battery but will need a load that will draw an amp (or two amps). The actual value doesn't matter as long as you can read it with the multimeter in series at the same time. Even powering a model via the wattmeter and a multimeter in series will do, although you may find there's too much volts drop through all those wires to allow the model to start up.

Chris Bott - Moderator25/05/2020 19:38:21
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Dennis, if you're still looking in, I've calibrated 3 new meters this evening and all 3 couldn't be adjusted quite enough on the current range. I can only assume that this batch of resistors have slightly different values to ones I've used before.

So, I had to alter the multiplier in the line measuring current to 45.
i.e:-
Amps = (((Atemp+LOOPS/2)/(LOOPS))*((1.1/1023.0))*45*TrimA)+0.11 ;

Dennis Mulhair25/05/2020 20:33:23
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Hi Chris,

Haven't got that far yet but still making progress. I ordered my screen very early on when Bitsbox didn't have any in stock so got mine from Ebay. As far as I could tell they looked the same as yours but the pcb seems to be bigger as it doesn't fit your box and there are more pinouts on mine!

Finally got it working using the following conversion table

Arduino pin no. motherboard socket pin No. New screen connections

VCC 1 VCC

GND 2 GND

8 3 CS

9 4 RST

10 5 RS

11 6 SDA

13 7 CLK

I am at the stage of setting the input voltage on a 3 decimal place digital multimeter which seems very stable. I'm using a 1 cell lipo to set this, will attempt the current setting tomorrow. Will come back to you with my findings.

Regards

Dennis

Dennis Mulhair25/05/2020 20:36:07
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The spacing of the table didn't come out as expected when I uploaded it. Example:

Arduino Pin No: =VCC

Motherboard socket pin number: =1

New screen connection: =VCC

Chris Bott - Moderator25/05/2020 20:37:50
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Blimey, that's a complication you could have done without. Well done on persevering. I look forward to seeing your finished unit.

Dennis Mulhair26/05/2020 10:10:24
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Hi Chris,

I’ve noticed occasionally that after switch on I’m getting a white screen, to restore the program I’m having to use the reset button on the Arduino to get the program to start. Have you come across this before?

Dennis

Chris Bott - Moderator26/05/2020 10:25:59
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Hi Dennis,

No, I always see a white screen for a second or two, then that gets replaced by the expected screen. I've never had one stick at white.

Dennis Mulhair26/05/2020 11:35:08
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Hi Chris

Just gone through the current setup and the unit is reading high, see below

5.54V------- Meter reading 0.530A---------Ardunio reading 0.53/0.58A

7.64V------- Meter reading 0.730A---------Ardunio reading 0.80A

10.26V------- Meter reading 0.991A---------Ardunio reading 1.06

This was with the current pot at its lowest setting. I am going to load your mod above and come back with more results

Dennis

Dennis Mulhair26/05/2020 11:50:27
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H Chris,

Thats got it. Current readings now matching the digital meter.

Now to fit it in the box.

Dennis

Chris Bott - Moderator26/05/2020 12:33:38
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That's great news, thanks Dennis.

Dennis Mulhair26/05/2020 14:48:36
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finished unit.jpg

Dennis Mulhair26/05/2020 14:49:12
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Works well and accurate.

Chris Bott - Moderator26/05/2020 15:02:43
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Looks great. You're right, the display does look the same. What a shame the pinouts are different.

Phil Olson - Model Technics06/06/2020 20:09:55
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Just in case anyone has a problem I had to install the Adafruit VEML6075 and Adafruit BusIO libraries as well as the GFX and ST7735 in Arduino to get it to compile without errors

Edited By Phil Olson - Model Technics on 06/06/2020 20:10:14

Chris Bott - Moderator06/06/2020 21:57:15
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Thanks Phil. Useful info. I guess I installed those a while ago.

Phil Olson - Model Technics09/06/2020 09:56:07
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not quite finished but at least it works ( I got my display from ebay !!)wattmeter.jpg

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