Digital Oscilloscope for Testing & Debugging Astro Remote Controls

[Gina]

I've ordered a USB charger from Hobby Electronics with Royal Mail 1st class delivery, so with any luck they'll send it tomorrow and I'll get it Saturday.

[ringz]

I bought some of these:

http://www.ebay.co.uk/itm/5pcs-TP4056-with-Battery-protection-LIPO-Charger-Module-Board-Micro-USB-TE420-/301905672102?hash=item464afaf7a6:g:YecAAOSwneRXQqwy

Okay with 1 cell.

[Gina]

Well spotted - I have ten of those coming from China but a single more expensive charger from the UK.

[Gina]

I have been looking at the layout for the power board and find the components will easily fit on one of my standard stripboards.  This board will go behind/underneath the main PCB with the battery accessible from the back of the unit.  Associated switch and LED will go at the front, of course.  I expect to be designing the case shortly.

This photo shows the power board sitting beside the main PCB on the table.  The piece of red card represents the size of the Li-Ion cell charger.  There are a few other components to go on the board such as the crystal and capacitors for the ATMega328P chip and resistors for the LED.

[Gina]

[Gina]

The bi-colour LEDs arrived this morning and I've been doing some testing.  Even though they are diffused, the red and green sections show as distinct patches within the LED and having both on for yellow or orange is not as nice as I would like.  I think I shall go for individual green, yellow and red LEDs.  I might go for more than three as there are plenty of outputs from the ATMega328P chip so it only adds LEDs and resistors plus a bit of wiring.  I think it might be nice to give a better indication of how much charge is left.

[Gina]

Been looking at the ATMega328P chip and have found that for applications that are not time critical it is possible to do away with the crystal and capacitors and use an internal clock, thus reducing the component count still further.  The method uses a chip without bootloader preloaded and uses an Arduino Uno to load a different bootloader for the new clock source.  ATMega328P chips are much cheaper without bootloader too

Many of my projects could use just the ATMega328P chip and most aren't timing critical.  With the problems Arduino Nanos seem to have with the UART chip for USB I think bare AVR chips could be a better solution.  Without the extras in the Nano the supply current will be lower.  In a lot of applications the chip could be run directly from a Li-Ion cell.

[Stub Mandrel]

Take a look at Atmel Studio 6, it's a bit mindblowing compared to the Arduino interfaces. I use it with an AVRISPII for programming without a bootloader. You need to include a 6-pin ISP socket on every board - but if short of pins you can use this as a connector for a keypad/serial inteface etc. and just swap connectors for programming. Studio comes with GNU CC which I'm sure you will be able to use.

The AVRfreaks forum is good for helping beginners but they do get shirty if you don't do things the 'optimal' way and they are very wary of assembly language addicts :-)

[Gina]

Thanks Neil   I think I'll stick with Arduino programming though.  I would have happily taken on a new language or IDE in the past but my talents are not what they were, I'm afraid.  Plus I think I can make better use of my time.

[Gina]

USB charger arrived today so that's another part towards the job

[Gina]

That was a half amp USB charger and today a 1A battery charger arrived plus a packet of coloured LEDs.  I think 5 discharge levels should be enough.  I'm thinking of having one LED on at a time with blue showing fully charged through the colours shown to red representing need to recharge "now".  One LED on at a time will reduce battery discharge level display current.  I think the 1A charger may be more appropriate for a 4AH cell than 0.5A but I haven't really decided yet.

[Stub Mandrel]

0.5A will be just right for an overnight charge.

[Gina]

Yes, that's true and the half Amp charger has a standard mini USB socket on it - the 1A charger has a strange input connector plus solder pads so would need a connector added.

[Gina]

Circuit for battery charge level display with 5 coloured LEDs.

[Gina]

I'll choose the resistor to give reasonable brightness on the dimmest LED then the others can be brought down to the same light level using PWM.

[Gina]

I'm wondering if the battery charge level display would be appropriate to charging as well as discharging but that would mean the battery would always be connected to the ATMega328P and LED and hence constantly draining though admittedly at a low level.

Here are the two different battery connection and switching circuits.  The first showing charge level only when oscilloscope switched on and the second continually.   The DPDT toggle switch will actually be a centre off variety.  CHARGE-OFF-ON

[Gina]

I've ordered a slide switch for the battery/power switch rather than using a toggle switch as it will match the other switches and will be easier to fit.

[ringz]

With the charger modules shown above there are terminals for the battery and for the device you want to drive so you wouldn't need a switch with one of those.

They also have battery protection built in so you can use cheaper cells.

Martyn.

[Gina]

Battery board layout.

[Gina]

17 hours ago, ringz said:

With the charger modules shown above there are terminals for the battery and for the device you want to drive so you wouldn't need a switch with one of those.

They also have battery protection built in so you can use cheaper cells.

Martyn.

I would still want a switch for ON and OFF.

[Gina]

Battery board completed plus small board for the LEDs.  Waiting for the power switch.  Can't design the case until I've got all the bits.  It won't be easy with all the different levels.  I'm wondering whether to get the plastic box kit and add to that, just using whichever parts are suitable.

[Gina]

Had a look for the acrylic cases and considering what is included and the saving in time and effort, I decided to buy one from Amazon UK - due for Prime delivery tomorrow.  Acrylic DIY Kit Case Cover Shell for DSO138 Oscilloscope

[Stub Mandrel]

Think I'm going to have to invest in one of these scope boards..

[Gina]

The case kit arrived this morning and looks good.  I shall now be assembling it around the oscilloscope parts.  No switch yet so can't finish the whole thing today.  I'll post photos as I proceed.  Here's what I've got and showing the box fitted together.  The protective paper needs removing and I'll assemble it on a clean sheet (of something) to avoid scratching the surfaces.  Not that scratching is impossible during use (or soldering iron burns ).

 

[Gina]

Backing paper removed from main acrylic parts.  Difficult to start but a sharp craft knife under a corner helped.