The NiMH solar rechargers saga continues….

The one thing holding me up on doing the tutorials for the rechargeable NiMH circuits is the global semiconductor shortage.

location for the LM317LZG to-92 package – no room for the larger T0-220 package

The AAA recharger version doesn’t have much room and so needs to use the TO-92 version of the LM317 voltage regulator. As you can see, there’s not enough room for the larger TO-220 package

Here’s what the TO-92 package looks like:

TO-92 package

I ordered a bunch from Farnell and was initially given a delivery date of Dec 17th (2021) but, as the day approached, it shifted to Dec 26th… then Jan 7th, then Jan 21st, then Jan 31st and it’s now at Feb 7th.

So I’ve ordered some from ebay and when they arrive (tomorrow?) I’ll cancel the order with Farnell.

I’m not happy about the delay but I have managed to make progress with other projects while I’ve been waiting.

The prototype solar tracker is now in its final version and I’ve been playing with some 1W warm white LEDs to use with the batteries it’ll charge. That way I can use them in place of some of my mains-powered lighting, helping a little to reduce my carbon footprint – and save money on electricity bills at the same time. Nice!

Watch for blog posts about them both.

The saga of the solar charger for NiMH batteries

I’ve been working on a project (coming very soon) in my solar / renewables series that lets you charge NiMH rechargable batteries.

What a journey! Here’s a prototype I built to help me visualise the way forward:

photo showing the prototype AA NiMH solar charger
prototype AA NiMH solar charger

The challenges to overcome are that the batteries come in two different sizes – the smaller AAA and the larger AA ones. More than that, they come in lots of different capacities and each capacity has to be charged at a different rate.

Another complication is that the solar panel needed depends both on the number of batteries to be charged and the charging current – Ohm’s law tells us that the solar panel power needed is the total battery voltage x the charging current.

Coming up with the most practical combination for the project with all those variables proved to be a real mind bender.

Way forward

In the end, after much checking of physical sizes and layouts of the charging circuit compared with the available space in AA and especially AAA battery boxes, I decided on two projects – a solar charger for:

  • 2 x AAA batteries that can be switched to charge two different capacity batteries (as decided during the build)
    With space being so tight, I’ve had to use a lower power and hence physically smaller LM317 constant current device. It’s ok in the lower power version because the maximum practical capacity for AAA NiMH batteries means a charging current well within its maximum power dissipation rating.
  • 2 x AA batteries that can be switched to charge two different capacity batteries (as decided during the build)
    A suggestion section in this second project pointing the way to allow 6 batteries to be charged, mix ‘n match AA and AAA (as long as the capacities are the same), and having the circuit cater for more than two capacities.

Size comparison

Here’s a comparison of the size of the lower power version (TO-92 package) on the right, with the higher power one (TO-220 package) on the left.

a photo comparing the sizes of the two LM317 packages
higher and lower power packages of the LM317 compared

With so little space to play with in the AAA battery case, you can see why it’s circuit needs to use the lower power version!

To help get my head around things, here’s the table I put together covering many of the commonly available battery capacities, the resistors needed to set the manufacturer-recommended C/10 safe charging currents for them and the resulting solar panel wattages:

Battery Capacity (mAh)R1 value (Ω)C/10 charging current (mA)2 Battery 6V Solar Panel6 Battery 12V Solar Panel
50015 + 10500.5 Watt1 Watt
70018690.5 Watt1 Watt
80010 + 5.6800.5 Watt1 Watt
90010 + 3.9900.6 Watt1.5 Watt
100010 + 2.7980.6 Watt1.5 Watt
13008.2 + 1.51290.9 Watt1.8 Watt
20004.7 + 1.81921.25 Watt2.5 Watt
23003.3 + 2.22271.5 Watt3 Watt
24002.7 + 2.72311.5 Watt3 Watt
25003.3 + 1.82451.5 Watt3 Watt
28003.3 + 1.22782 Watt4 Watt
29002.2 + 2.22842 Watt4 Watt
resistor value(s) and solar panel watts for manufacturer-recommended C/10 charging

Tip for ‘exposing’ LEDs

I’m sure I’m not the first but I’ve not seen anyone else doing this. Have a look at the photo at the top and you’ll see two holes in the battery box lid to let the LEDs show through.

If you look closely, you might notice that they’ve been filled with uv glue. That way, the LEDs can still shine through but water / dust won’t get into the box.

It’s simple to do – just drill a couple of holes and then stick some sticky tape on the underneath. You can now fill the holes with uv glue and it won’t run away while you set it. Once set, just peel away the sticky tape.


Where is Moji? A fun early-learners’ game app for iOS and Macs

I’m on a roll! After developing the More or Less app, it was easy for me to develop this new one.

Who is this game for?

I’ve aimed “Where is Moji?” squarely at early learners / younger pre-schoolers. It teaches them a critical skill: to recognise and then find one pattern hidden amongst a screenful of others.

To make it fun, I’ve chosen the emoji used in the game from

  • sports
  • animals and nature
  • transport
  • everyday objects

Dad and / or Mum can sit in and help them learn the names of the animals when they come up. Lots of learning opportunities are there to use.

For even more fun, when they find Moji, they’re rewarded with a funny cartoon sound and a visual reward of a fountain of coloured circles, cascading down the screen.

I’ve designed it so that the early runs and levels have fewer emojis, with the number increasing as the game progresses. If you’re feeling adventurous, you can try the setting for a big kids game, which has far more emojis and a faster bonus multiplier countdown,

The easy and hard modes I’ve included for both the Kids game and the Big Kids game means there’s always a challenge. What’s the difference? The hard mode has more emojis and a faster countdown so even if you have a great reaction time, you’ll struggle to hit the top scores.

Get yours…

Download “Where is Moji?” here:

See screenshots of the game and a demo video

When you start each run, the screen shows you the emoji you’re to find.

When you’re ready, tap “Go” and the level begins. Note that the emoji you’re to find is repeated just above the “Go” button in case, in the excitement of it all, you forget what you’re to find!

Kids Game: The emoji they’re to find is also shown in the scores panel

Take a look at this screenshot of the last level of the Kids Game (on the easy setting). It shows how the number of emojis has increased:

Kids Game: Run 4, Level 5

If you like, watch this video of a complete game being played on an iPad. It goes all the way up to getting on the high score table – with the cheer you hear when you do! (I’ve included a different high score table for BigKids, to keep them seperate.)

A complete Kids Game (on the easy setting) being played on iPad

Thinking about building an iOS app for Zazzle

We’re not quite sure what we can achieve via an iOS app and Zazzle so we’ve been digging around and having a play.

As part of that we developed a simple and fun app for iPhones and iPads aimed squarely at kids (big kids, too!)

It’s called More or Less Kid’s Game and teaches older preschoolers about the notion of more and less in a fun and exciting way.

Here’s a screenshot showing the core in action. In the previous screen to this one, the player was shown one of two emoji.

In this case (though you can’t tell) they were shown a flamingo. Now they have to decide whether there are more or less flamingoes than rhinos by pressing the More or the Less button. (Yes, we know it really ought to be more or fewer but we’re practicing being less pedantic!)

a screenshot of the main gameplay area of the More Or Less iOS app
A screen from our More or Less iOS app

If they don’t make up their mind quickly enough, after a short while the bonus multiplier starts to count down and the potential score for a right answer reduces.

If they choose correctly, they get a positive, funny cartoon sound and a visual celebration as a reward. The run score they get (the bonus multiplier X number of images) is then added to the total score for the level.

If not, they still get a funny cartoon sound – but no visual celebration and no score.

There are 5 levels and 4 runs per level.

If they play with Dad or Mum at their side, they can get help counting the emoji to find out whether there are more or less.

We’ve made it so that the earlier levels have fewer images with bigger differences between the numbers of each. As the game progresses, each level has more images and smaller differences between the numbers of each emoji shown.

Get More or Less here on the app store.

How can I get people to promote my Zazzle store?

We’ve added a new feature to Nifty to help your Zazzle store get promoted. You can now submit your store for promotion by the affiliates / artists that use Nifty as part of their promotion strategy.

screenshot of the store submission form
screenshot of the store submission form

When anyone submits a store, they’re first asked to pin/tweet/share 20 designs from a store that’s been submitted previously (chosen at random).

So there’s two ways to get promoted when you submit your store to Nifty, by:

  • affiliates using the new “pot-luck” button in the Nifty Promo Control Panel
  • someone submitting a store after you and your store gets chosen as the one to have its 20 products pinned/shared/tweeted

All good quality stores are welcome. Submit yours if you like – the sooner the better! If you think about it a bit, it’ll make sense…. stores submitted earlier have a slightly better chance of being chosen.

Submit yours here