1S Wattmeter

[Chris Bott - Moderator]

You may have seen mention of a wattmeter designed especially for 1S indoor type models, in our favourite Scale column in the magazine?

I was developing this early in the year and got to a point where the "birds nest" construction was becoming unwieldy, so I designed a PCB and placed an order from China in mid Feb. These seem to have been lost in the post amid the current strange state of the world but the kind folk over at JLCPCB have refunded, accepted another order and sent these by DHL. So we'll see.

I'll keep this tread posted with progress. I may even need a little help to turn it into a fully finished unit.

It shows live Volts, Amps and Watts in the top section and Min Volts, Max amps and Max Watts in the lower section.

There's a 3d printed 3 section box consisting of a bezel section, an electronics section and an optional PP3 battery box / switch section for the back.

Without the battery box, it could be powred from an external battery, lipo or whatever is to hand.

[Martian]

Excellent Chris

[Biggles33]

I too think that's an excellent project and will be following with interest.

Could you maybe also say more about the JLCPCB suppliers and the process involved, if that isn't being too nosey please? i.e. what type of file(s) you need to supply to them, cost of the PCB in small numbers, is that for a basic PCB with etched tracks and holes drilled, or does it include screen printing etc.

Thanks.

[flight1]

here is a link to jlcpcb site lots of info , there are lots of other prototype pcb makers out there to. all very interesting

[Chris Bott - Moderator]

My PCB process is to use the free online design software at EasyEDA There's both schematic and PCB design available and the two are tied together.

Once designed there's a very easy clickthrough that takes you to their partners JLPCB. That transfers the files and you can go through the ordering processes.

Prices are really low. Say, $5 for 10 PCBs. Postage is more and now is probably not a good time to expect post to get through OK.

[FlyinFlynn]

Biggles - You will need to supply Gerber files to any PCB manufacturer. These are quite easy to come by.

Download and install EasyEDA. Produce your circuit diagram, then place your components in a PCB design. Once you are happy with that design (and ensure you ARE happy that it is correct) you can either obtain the gerber files from the program (it has a produce gerber files button), or you can order them direct from JLC from within EasyEDA. The cost is $5 for 10 small, standard boards plus shipping - of whichever shipping service you choose, although I believe your first order may be free standard shipping. This price is for professionally made double sided PCB's with through hole plating, double sided screen printing (if required) and double sided mask.

I have used JLC many times and have always been more than happy with the results and their service - just remember they are not responsible for the performance of the shippers! but as Chris has alluded to,and I can also confirm, JLC are reputable traders.

 

Nice project Chris, I will be following along with interest.

 

Beat me to it Chris!

Edited By FlyinFlynn on 18/04/2020 13:19:20

[Chris Bott - Moderator]

Snap - FlyinFlyn.

I don't even install EasyEDA. I just use it online and they store all my files.

Here's the schematic designed on EasyEDA

This is the screen that the PCB is designed on

And theres even a rotatable 3d view whenever you want to check it out.

Edited By Chris Bott - Moderator on 14/05/2020 18:10:06

[Biggles33]

Thanks Chris and FlyinFlynn,

That's exactly what I was interested to know. Can't believe it's only 5$ for 10 PCB's and double sided with through hole plating included. That's an absolute steal.

When I last dabbled with making PCB's using board from Maplin's, I think the bare board was £8 to £10 before you added the cost of ferric chloride etc etc

I wouldn't worry about added shipping delays from China, at least not based on my recent experience. Ordered a switch mode PSU from one Ebay supplier and a metal case from another on 27th March and one was delivered on the 8th April and the other on the 9th April.

Thanks again both for the info.

[Peter Balcombe]

This looks a very interesting project Chris.

What size display are you using? 1.44”?
i would have thought this hardware could easily be adapted for other things

[Chris Bott - Moderator]

Peter, it's this one, a 1.8" TFT from Bitsbox for a fiver.

[Mike Blandford]

Any reason why you need a separate power supply for the Arduino rather than use the single cell as the supply?

The ATMEGA328 still runs OK at 8MHz down to 2.4V, and you could use the internal 1.1V reference for the A2D converter.

Mike

[FlyinFlynn]

There are pro's and con's on both sides of the 'cloud' or 'local' storage debate. Everyone has their own preferences. I installed both the client and the auto-router as I found the on-line auto-router a bit flakey at times, probably due to it's workload and popularity.

I already have a slightly different display, THIS one has the same driver chip and specs but is a different pinout and footprint, so neither the PCB nor the .STL will fit! The best solution is to buy the correct display! For anyone else in the same boat and unsure of the different nomanclature it should be as follows -

CLK = SCK
Din = SDA
DC = A0
RST = RST
CS = CS

Chris, could you review your screenprint labelling? You have the 'IN' on the layout labelled as 'LOAD' in the circuit diagram, and 'OUT' negative connected to the circuits ground, that sounds backwards to me.

[Chris Bott - Moderator]

Posted by Mike Blandford on 19/04/2020 11:52:32:

Any reason why you need a separate power supply for the Arduino rather than use the single cell as the supply?

The ATMEGA328 still runs OK at 8MHz down to 2.4V, and you could use the internal 1.1V reference for the A2D converter.

Mike

Hi Mike I am using the 8Mhz 3.3v one but I think it was probably the display that gave up during the voltage dips.

Remember this is aimed at the very tiny 1S cells that the indoor guys use.

Of course if there's a way to dispense with the external battery than this could still be built that way.

[Chris Bott - Moderator]

Posted by FlyinFlynn on 19/04/2020 12:36:37:

Chris, could you review your screenprint labelling? You have the 'IN' on the layout labelled as 'LOAD' in the circuit diagram, and 'OUT' negative connected to the circuits ground, that sounds backwards to me.

I think you're right, FlyinFlyn - That will be one of the mistakes I was talking about.

It looks like the the -ve pad that is screen printed "IN" is indeed the junction between R1 and R2.

I wonder what else we'll find?

[GONZO]

USB

You can get various types of these USB units(I have a couple that I use) in different voltage , currents etc. No problem multiplying voltage and current for watts. Open and use different leads or USB and adaptors. Cheap, quick and simple.

[Peter Balcombe]

Posted by Mike Blandford on 19/04/2020 11:52:32:

Any reason why you need a separate power supply for the Arduino rather than use the single cell as the supply?

The ATMEGA328 still runs OK at 8MHz down to 2.4V, and you could use the internal 1.1V reference for the A2D converter.

Mike

Mike, a possible way to power from the 1-3S supply is to use a 3.3v output buck/boost converter module such as the 2.5v - 15v to 3.3v @600mA module available at present from Banggood for £1.41. Module appears to be 12x19mm which should fit in the battery space.

Chris, are you likely to be able to make your initial sketch available soon for others to try out on breadboard hardware before you have PCBs to hand?

[Chris Bott - Moderator]

Peter, I'll make everything available. The .stl files for the box and the sketch. Maybe the PCBs again so folk don't have to order 10 at a time. Maybe even kits with pre-programmed Arduinos if theres an appetite.

Please note that this is pretty much the first sketch that I've written from scratch so it's going to look very naiive to those in the know.

I'd like to just assemble one and try the sketch on it before I share anything though. I don't think it will be long.

Once shared, the combined knowledge on the forum may well suggest much better ways to do things.

[Chris Bott - Moderator]

Todays update on PCB shipping

[FlyinFlynn]

DHL!!!! get ready for the import charges.......

I have re-jigged the PCB for the display I linked earlier that I have....

The display solders on the back of the PCB with all the other components on the front. I also allowed for a piecs of nichrome wire for the sense resistor.. 16 gauge is 0.2956 ohms per foot at 68 degrees F...which sounds about right!

Gerbers are here but no guarantees!..I haven't built one either.

[Peter Balcombe]

Chris, presumably you noted that the J1 link on the back of the TFT panel needs to be shorted if running the unit from 3.3v (Bypasses the onboard 3.3v regulator for 3.3v supply operation). Just mentioned as it seems you were losing the display at low battery voltages.

The 47mOhm sense resistor will drop 250mV or so at 5A, but I assume you have accepted this for the sake of keeping things simple. (Otherwise you would need an additional device/higher supply voltage to boost the sense voltage).

[Chris Bott - Moderator]

Hi Peter, no I hadn't noticed that. I think that's exactly what this thred is about. I'm running the display and it's backlight from the 3.3V regulator on the Arduino.

Yes indeed, I'm trying to keep this as simple as possible. I have some ASC712 modules that work fine with little or no voltage loss. But they need a 5V supply.

So from what you've said about the display, would that also be fine from 5V?
Meaning another way to go would be to use a 5V Arduino with an ASC712 module.
(Taking up more space, obviously).

The use case for this is to compare and contrast powertrain changes in models running on just a few watts. The simple approach, hopefully just using a PCB track as the sense resistor, is perfectly adequate.

[Peter Balcombe]

Chris,

From the various data sheets/schematics I can find, it looks as if the TFT (LED pin) needs 3.3v max, but the VCC pin drives a data line level translator via a 3.3V regulator - thus allowing the data line interface to be 5v or 3.3v logic.

It appears therefore that you still need a 3.3v supply for the TFT display (LED pin), but can also use 3.3v VCC & logic , but then need to bypass the onboard regulator to ensure 3.3v. If it is a very low dropout regulator then it might not make much difference.

It did cross my mind that you could replace the 9v battery with a 2.7-16v input 5v buck/boost regulator & use this to drive a 3.3v Arduino via the Raw input as at present. Then you would then also have a 5v supply for an ACS712 or similar.

But as you say, you would need more board space.

[Peter Balcombe]

Chris, I found a zip file containing the 1.8” module physical dimensions, schematic, plus TFT & controller datasheets. Extracts of the TFT display voltage limits and schematic are below as photos. I can’t translate Chinese, but wonder if the first line is for the data interface & 2nd is the LED pin. If so, then the LED pin may be able to take up to 5v.

Hope this is useful.

Edited By Peter Balcombe on 21/04/2020 21:16:52

Edited By Peter Balcombe on 21/04/2020 21:19:29

Edited By Peter Balcombe on 21/04/2020 21:20:46

[Peter Balcombe]

Sorry Chris, just noticed that the TFT module on-board regulator is 3.0v, not 3.3v!

This sets the TFT display VDD in the centre of its datasheet range of 2.7-3.3v, whereas bypassing the on-board regulator would set it at the max. limit assuming the Arduino output is 3.3v Max. The CE6209 LDO regulator typically drops 60mV @ 30mA & 200mV @ 100mA, thus with a 3.3v (or higher) input voltage it is probably prudent to leave the regulator in circuit to retain the 3v TFT supply.

The Arduino Mini Pro regulator appears to be a MIC52xx series which appears to have a typical drop of 110mV @ 50mA & 165mV @ 150mA, thus the output is likely to droop if the RAW input goes below 3.5V or so.

I think there may be a level translator in the TFT (but not sure) else the data inputs would need to be protected (SD card has 1K series resistors on the input lines). The LED pin could run from a 5v supply, but probably a good idea to use a series diode to stay below the max datasheet level of 5v.

[Chris Bott - Moderator]

Thanks for all the input Peter

I have R9 on the PCB, intended to be linked out when using the 3.3v Arduino. But this could be used for a diode or series resistor when using different supply voltages. I'll stick with how I have it for now but it does look like there's room for experimentation.