The battery pack manufacturers are, in my humble opinion, scamming the general public into buying expensive battery packs when they don’t need to.
I’ve a Fujitsu Laptop that I use in spurts. Sometimes it’s in daily use being lugged around with me constantly, other times it gets left on the table under a pile of paperwork and not used for weeks at a time.
Recently I switched it on and the battery was flat and then found that it refused to charge. It’s around four years old so I thought that it had probably just come to the end of its life. The Laptop kept saying it was 98% charged but the charge indicator wasn’t illuminating.
I wondered if perhaps just one of the cells in the pack had failed (and the others could be useful for other things) but then I had a thought; I’ve seen this before with other so called “smart” battery packs. I took out my trusty Dremel power tool and carefully cut into the pack where I suspected the intelligent battery monitoring circuit was.
Once I’d cut into it, I could see the two connections going to the cells and placed a volt meter across them. The pack was reading 9.1v.
I set by bench top PSU to 11v and hooked it directly across the terminals. I applied power for around 5 seconds, removed it, waited a few seconds and repeated a few times. After each cycle I would check the pack voltage and slowly it started to climb. Once I got the pack up to around 10v, I quickly inserted it back into the laptop and switching on the power. Hey presto, after a couple of seconds the charge indicator came on and Windows reported the pack was 4% charged… and charging. I left it charging whilst I got on with other activities keeping a fairly close eye on things (these retched batteries have a habit of catching fire) and after around 90 minutes or so, Windows reported the pack was fully charged and this was confirmed by switching off the mains power and the laptop happily running on its battery pack whilst reporting around 90 minutes of run time available. This is about right for this laptop.
I've got a thing for clocks... I wonder if it's because I'm not getting any younger.
Anyway, I had a day free over the weekend and decided It was clock building time.
There's not much to this clock really. A PIC18F25K22 running some simple firmware written in AMICUS18 BASIC. There's a Dallas DS1302 RTC chip with battery backup, and a handful of other components.
I've been experimenting with different firmware to see which makes the display the most readable.
The image on the left of the clock front is showing a time of 10:20:13UPDATE 29/10/13
I've created a construction project for this clock which can be found here.
Whilst attempting to repair a simple microphone pre-amplifier for a friend, the culprit was found to be a blown transistor. A quick internet search found the specifications of the device and it was then a simple matter to find a suitable replacement from what was available in the junk box.
Interestingly, my friend, who has only a casual interest in electronics, was bemused by all the Vcb, Vce, Ic and other details in the parameter tables.
So I did a quick drawing of a simple common emitter amplifier based on a NPN transistor and explained the different values.
Below is a sample specifications table for some NPN transistors. Notice the three BC107 transistors at the bottom of the list are from two different manufacturers, but their specifications vary quite a bit. For example, the Hfe (Small Signal Gain) of the TRU device is over four times that of the CDIL variant, but the CDIL variant has a higher maximum working frequency.
The parameter that most hobbyists are concerned about tends to be the Ic. This is the maximum current that the transistor can drive when a load is connected between the Collector and +Vcc.
Summer is finally here in the UK, and to celebrate the good weather, a friend and I were sat outside in the back garden chatting whilst drinking beer and eating BBQ, and as it started to go dark I got sight of a bat.
I built a bat detector some time ago but never really got a chance to try as the bats seem to have left.
Fetching the detector from the workshop, I pointed it at the trees, switched on and waited… and waited… and waited… eventually some quick audio bursts were heard and we saw the culprit fly past; doing some rather impressive aerial manoeuvres as it happens whilst catching his dinner.
So, I know the detector works, but the next job is to increase its sensitivity – that’s this weekend’s project.
Once it’s done, I’ll post up the circuit here.
The weekend came... the weekend went... as did the summer.
Looks like I'll have to try this again next year.