1S Wattmeter

[Chris Bott - Moderator]

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 Mulhair]

Chris, Is the software in the Dropbox contain the latest updates?

Thanks.

Dennis

[Chris Bott - Moderator]

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

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

[Dennis Mulhair]

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 - Moderator]

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 - Moderator]

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 Mulhair]

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 Mulhair]

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 - Moderator]

Blimey, that's a complication you could have done without. Well done on persevering. I look forward to seeing your finished unit.

[Dennis Mulhair]

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 - Moderator]

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 Mulhair]

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 Mulhair]

H Chris,

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

Now to fit it in the box.

Dennis

[Chris Bott - Moderator]

That's great news, thanks Dennis.

[Dennis Mulhair]

[Dennis Mulhair]

Works well and accurate.

[Chris Bott - Moderator]

Looks great. You're right, the display does look the same. What a shame the pinouts are different.

[Phil Olson - Model Technics]

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 - Moderator]

Thanks Phil. Useful info. I guess I installed those a while ago.

[Phil Olson - Model Technics]

not quite finished but at least it works ( I got my display from ebay !!)

[Chris Bott - Moderator]

Excellent, it's really nice to see the fruits of a design when it's put together by someone else. Thanks Phil.

[Dennis Mulhair]

Hi Chris, could you explain an anomaly I have come across. I am running the units on V4 software and have noticed the “Min Volts” is recording what appears to be the maximum voltage of the cell. I was expecting the cell voltage to drop in use and with a volt meter across it it does, but the Wattmeter is still recording the higher voltage that was there at switch on. The “volts” value faithfully follows the state of the voltage on the cell.

I replaced the 1 cell with a power supply and the unit was the same. When I lowered the voltage on the supply the wattmeter only recorded the higher initial voltage in “Min Volts”, but if I increase the voltage (something that would not happen in the real world) the “Min Volts” alters to reflect this increase.

Are we recording the Max voltage of the cell, and so should the labelling change to “Max Volts”?

Regards

Dennis

[Chris Bott - Moderator]

Hi Dennis, I have to leave the house in 5 mins do this is off the top of my head.

I (think I) have it saving all 3 readings when power is at a max.

I did try recording all 3 independently, when they hit max or min. But often found apoarent anomalies between the saved max watts and the multiplied max amps and min volts.

Would this explain what you're seeing?

For the intended application, I think saving all 3 with a single trigger makes sense? What do you think?

[Dennis Mulhair]

Hi Chris, so if the value is that at "Max Power" maybe the Min Volts & Max amps be relabelled to MPvolts & MPamps? At the moment its a bit confusing.

Dennis

[Dennis Mulhair]

Then again I suppose if I was measuring in the real world using say a 1 cell LIPO and an actual motor and esc the readings would make more sense. I will try this tomorrow.

Dennis