Posts Tagged ‘electronics’

Little surprises in electronics.

October 4, 2014

On a cheap Yuan Hung Lo MR16 LED lamp, it was a pleasant surprise to find silkscreen print on the tiny PCB showing the orientation of the surface mount rectifier diodes.

SMT diode replacement on a MR16 LED lamp.

SMT diode replacement on a MR16 LED lamp.

I had taken a photo of the board before starting work, and I will be cleaning off the flux before putting the lamp back in to service. At this stage I had only replaced two of the four diodes.


A little note about the batteries for the Philips SHC5100 wireless headphones.

November 22, 2012

The gist of it is don’t rush out and buy the specific part (HB550S).
Buy a pair of regular (Nickel Metal Hydride) AAA size rechargeable cells, try and aim for about the same capacity of 550mAh. Then carefully cut about 3 or 4 mm of the plastic wrap from the negative end of the cell.
Have a look at this image for a guide.
Remember that most of the metal can is the negative electrode, so be careful to prevent accidental short circuits with the extra metal exposed.
If you look in the battery compartment of the headphones, there is an extra metal finger which contacts the battery on the side. This is how the headphones detect if the battery is the rechargeable type.

TomTom One temporary mains power supply.

April 27, 2012

I doubt this would be recommended by either of the manufacturers involved (TomTom or Exposure).

I notice that the mains charger for the Exposure MaXx-D can also power a TomTom One (No longer supported by the manufacturer).

This is useful if you have a TomTom One which has been sat at the back of a cupboard for some months, and the internal charge on the TomTom’s battery has self-discharged. You have a choice of finding (or bodging) a mains charger, or going out to the car at 11-something-pm on Friday.

Secret indicator on the Camsports HD-S 720p

September 22, 2011

I noticed something about my “bullet cam” recently. There is a indicator LED within, which can only be viewed from the back of the unit. You have to point the lens almost vertically down, and look in the left mystery hole on the back.
Like this
I am not sure if it means the camera is on, or means the internal battery is charging. I’ll try to remember to check it after it has charged fully. The manual makes no reference to this “undocumented feature”. You can download the manual from the manufacturer’s own site.
Actually there are number of ways the camera’s behaviour differs from the instructions:

  • The LED next to the lens does not flash blue when recording starts. The manual says it does.
  • Quote “When recharging, the LED record indicator will be red. At full charge, the LED will turn green.” When re-charging (with the mains adapter) the record indicator does not light. At full charge, there is no indication at all that charging is complete. When the camera is full of data, the record indicator alternates red/green. It also beeps about eleven times before shutting down.

It won’t be first time I’ve encountered a gadget whose behaviour differs from what the manual claims, not that it detracts from the results I’ve had from the camera. With so many embedded systems around these days, I think we should be more aware of the fact that the behaviour depends on the internal software. As a consequence we should not assume that the behaviour will always be consistent because there may still be bugs in the software.

Edit: The secret indicator LED is definitely a “charging” rather than “on” indicator.

HDMI cables: Brands don’t matter.

May 15, 2011

This is some (vaguely) scientific research, and it reaches a conclusion I’ve strongly held to be true for many years.
I would venture to suggest that the more expensive HDMI cables, which tend to have heavier connectors at each end, may contribute to the premature failure of the fragile HDMI ports on the back of modern LCD TVs.

Fixing the car key fob.

April 18, 2010

I found myself replacing the battery in my mother’s car key fob. The car is a 2001 Vauxhall/Opel Zafira. When I had prised the key part from the electronic transponder, and was about the remove the battery (a common CR2032) I noticed the battery holder seemed to be a bit more mobile that I would have expected.
Then I spotted why it was loose. I suspect it’s a result of years of use, the negative pin of the battery holder was just sitting in the hole on the PCB. Making a poor and intermittent contact.
That explains lots of things. It explains the poor range on the radio, it explains why the key fob often needs re-synchronising with the car.
So I set-up the soldering iron, and removed the old solder from the hole, re-flowed in new solder. Now the key fob works well, and the range has noticeably improved.
I wouldn’t like to say how much the local Vauxhall dealer would charge for a replacement key fob, particularly when they charged 7UKP for a 2UKP battery a year ago.

P.S. To re-synchronise the key fob; use the key to open the driver’s door. Insert the key, check mother hasn’t left the car in gear (bad habit on the flat), turn the key to the second position. Hold the ‘lock’ button until you hear the doors lock and unlock. Remove key, job done, look smug.

A simple solar-powered electronic project.

April 7, 2010

I recently made a solar-powered night light, and I thought it would make a good electronics project for anyone who is starting to learn electronics.

I acknowledge and am grateful for the information provided by Evil Mad Scientist Laboratories here.

The circuit diagram is here. Considering it from left-to-right, a solar cell charges a 100F capacitor through the diode D1. The diode prevents the capacitor from discharging when it is dark.
The 4k7 resistor provides a sense voltage to the base of a PNP transistor T1. (Rule of thumb: PNP transistors conduct from emitter to collector when the base is pulled low)
In the dark, T1 allows current to flow (via a 100 ohm limiting resistor) to the Joule Thief.
The Joule Thief is a simple switching boost mode power supply, although its’ theory of operation is quite complex. For most purposes, I consider it as a “building block” or a single component. The double-wound coil, the 1K resistor, T2 and D2 (white LED) form the Joule thief. The LED is not actually on continuously, it flashes at some silly fast number of pulses per second. This frequency depends on the input voltage, the nature of the coil and the transistor T2.
I had made the Joule Thief separately, on a bit of strip-board. In these pictures here, here and here you can see it.
The control part of the circuit I made by connecting the components directly together, for simplicity’s sake. Using a bit of heat-shrink here and there to prevent short circuits.
The entire project is in a transparent plastic box, which may have been one of these. I used a few dabs of silicone sealant to secure some of components in place, a bit of sticky tape for the solar cell.
Finally, when soldering to the solar cell, use extra flux and heat the solder just enough – don’t hesitate to remove the soldering iron when the solder flows.

17/6/2010: A quick update.
If you don’t fancy winding your own coil, “acquire” a miniature isolation transformer from a dead PCB.
Something like this:
Although they come in various different designs, I found one in a faulty ADSL line filter recently*.
Ideally it will have a 1:1 ratio of primary to secondary windings, but you may have to guess at the relative polarity of the coils, test it on breadboard first.

* The transformer I used came from a “Tehkal/Origo ASL 2019” (this page, about half-way down. It did explain why the connection would sometimes drop when the telephone rang.

When tracing a power fault on a laptop…

July 18, 2009

… check the power supply first. 🙂

If, like me, you decide to disassemble the laptop first, it will probably turn out to be a waste of time An educational waste of time perhaps.

Free phone upgrade for me!

July 8, 2009

My Nokia N95 started acting oddly just over a fortnight ago, eventually I took it to the shop where I had signed up to the contract. “We’re very sorry but we’ll have to send it to a service centre”.
Ok fine. One week later, (that would be yesterday) I had a phone message to come to the shop about my phone.
I rushed there today, to be told that my N95 was broken beyond sensible repair, and Nokia were giving me an N96 as a replacement. Result!
I admit I’m not quite sure what the differences are, although the N96 has more internal memory and it has a micro SD slot. The N96 keyboard is a little larger too, I like that.
While I was in the shop, reclaiming my deposit for a loan phone, the assistant said that the other way to get that phone was with a £75 per month contract. Currently I pay a little less than half that.

On cheap cables.

July 5, 2009

I took this photo as way of expressing one of my pet hates:
A cheap HDMI cable, with the receipt showing the price.
In this bold age of digital everything, we can save some money on cables. Consider that HDMI (like S/PDIF) is a digital interface, and as such it will either work, or it will not. In the home we tend to use short cables to connect our gadgets together, so we don’t usually need to worry about signal degradation associated with long cable runs.
So why is it we’re spending so much money on “premium” cables? For a 2 metre cable it’s a complete waste. There’s no difference in the quality of the signal and content as it is transmitted. This is particularly true of HDMI where there are lots of checksums to detect ‘tampering’ because of Hollywood’s paranoia about piracy.
There are certain manufacturers* which claim their uber-HDMI cable will give you “more realistic colours, less blurring on movements, and a more 3-dimensional image.” Sorry, this is utter false-hood. The signal integrity checking within the HDMI handshake will ensure the exact same image is transmitted. If your display device makes it look poor, then an expensive cable won’t fix it.

* They are likely to resort to litigation rather than science to defend their claims, but there are lots of them about.

I’ve even read reviews in “Which?” magazine claiming that some S/PDIF cables sound different to others. Honestly, will you take a step back and think about what you’re saying?

It may matter if your various A/V components are long distances away from each other, over and above (say) five metres. Or if you know your home-cinema room has a problem with radio frequency interference, it might help. The only other situation where it does matter is where analogue signals are concerned, even then you have a sliding scale of diminishing returns on the performance versus the money spent.