The HumanaLight – A Flashlight That Uses Your “Dead” AA Batteries

A couple of weeks ago, I was spending a very pleasant hour or so waiting in the front yard for the mail carrier to deliver some packages of vintage radio parts I had ordered a few days earlier. My neighbor’s cat Stephen was lounging around with me, and it was one of those perfect afternoons where time almost stands still. It was warm, with a slight breeze and as Stephen and I lay on the garden path looking up at the sky, I nearly forgot the reason for my being out there in the first place.

Eventually, the mail carrier arrived and Stephen took off. He’s an indoor/outdoor kitty, so mistrust of humans he doesn’t know is a valuable trait. The mailman handed me two packages packed with vintage dials and other parts – and another, smaller packet from my friend Thomas Witherspoon K4SWL. Inside was a kit to build the HumanaLight – a flashlight that uses the residual energy in depleted AA batteries to provide useful light for much longer than would be possible without this neat circuit –

The HumanaLight is based on the “Joule Thief”, a self-oscillating voltage booster that boosts the low voltage from a nearly depleted AA battery in order to light an LED. It does this, of course, at the expense of a greater current draw from the battery but it’s not as if this energy was going to be used otherwise.

Thomas is the founder and director of Ears To Our World, a non-profit organization whose main goal is to empower people living in extreme poverty or war-torn areas of the world by distributing self-powered short-wave receivers to them. It may sound like a simple thing, but for people living under very difficult circumstances, access to reliable news and information from areas directly outside their own can be a lifeline.  This page explains it more succinctly.  Many of the radios that ETOW distributes incorporate LED flashlights, and it was noticed that this feature of the radios is very popular. If you don’t have reliable electrical service, a flashlight that can be powered by hand-crank or batteries charged by solar cells is a very useful thing to have.

The HumanaLight was inspired by the LED lights on the self-powered radios distributed by ETOW. It’s a neat idea – a little LED light that is powered by a novel power source – the residual energy in nearly-depleted AA batteries. When the voltage in the AA cells you are using to power your portable radio, camera, or other device, has dropped so low they will no longer power it, there will most likely still be enough energy  in them to run this little flashlight for a useful length of time.

The HumanaLight comes with an easy to follow set of step by step instructions for assembly. It would be an ideal kit for a beginner –

Stephen strolled along to see what was going on and decided to inspect. Luckily, it passed the whole process without a scratch –

Taking a brief break from the rigorous quality control process –

Assembly is simple – just a few components to solder into the board and bingo – you’re done!  The kit comes with two white LED’s – a standard size one, and a jumbo one. You also have the choice of mounting the LED either with the leads bent at right-angles so that the LED points forward like a flashlight, or you can solder it flush with the board so that it points upward. I couldn’t decide, so I didn’t solder it in at all for these pictures, just placing the LED through the mounting holes without soldering (I later decided on using the jumbo LED and soldering it in flashlight-style).

For comparison, I first plugged in a fully charged NiMH cell with an unloaded voltage of 1.35V. You can’t really get an idea of relative brightness from these photographs, as the LED completely blows out the highlights but here’s the picture anyway –

I then tried an old battery that measured 0.76V unloaded –

You can’t see it too well in the picture, but the “dead” battery gave noticeably less intensity. However, if I was in such a situation that I needed an emergency light, and all I had were a few nearly exhausted batteries, I’d be glad for this much light to see my way around. I had another cell in a similar state of depletion, but no others to try. I have read comments from others who tried AA batteries with unloaded voltages of ~0.4V that didn’t work. This circuit does usefully boost the voltage available from a near-depleted cell but it obviously has limits. A cell with an unloaded voltage of ~0.7V isn’t useful for much though, so it’s great that you can use the HumanaLight to get some useful emergency light from it.

The board has a handy hole at the opposite end from the LED – no doubt for a lanyard or suchlike. You could also use it to hang the HumanaLight on a nail on the wall for easy access during an emergency. It would be fun coming up with an enclosure for this – perhaps some thin-walled tubing. I have left mine as is. I plugged a freshly-charged cell into it and switched it on Friday night. Although not an intense beam (it is, after all, a single LED) it raised the ambient light level in my room enough to make it a bit harder to get to sleep, so the next morning I moved it into the hallway where it remains. I’m keen to know how long it lasts.

The HumanaLight is available from Universal Radio here. With circuit design by Gregorgy Majewski and board layout by David Cripe NM0S.  It’s a neat kit and if, like me, you believe that shortwave radio is still a very relevant and useful way to get news and information to people living under very difficult circumstances, purchasing it is a great way to contribute to the cause.




5 thoughts on “The HumanaLight – A Flashlight That Uses Your “Dead” AA Batteries

  1. Hi Steve, this circuit or the Joule Thief was described in PW in an article by George Dobbs a few years ago.

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