Sunday, 27 November 2016

Mini Oscilloscope


Bought this mini oscilloscope as a kit on eBay (from China as usual) for £20. The main board with the surface mount components was already completed, but the electrolytic capacitors, an inductor, diode and all the switches had to be soldered in along with the display. There is no case as such, but clever use of 2 extra pieces of pre-cut PCB and 4 stand-off fixings make for a nicely finished unit. I might make sides for it out of 3mm foam board if the notion takes me.

When I initially switched it on, nothing much happened except the backlight was on. Checking the troubleshooting guide helped and it turned out that the potentiometer for adjusting the LCD contrast needed a bit of working up and down to clean its track.

The 'scope can measure up to 2 MHz which is fine for my needs and has sample and hold and a frequency meter function. I tested it with the composite video signal from my Arduino TV-Out board and got a nice sync waveform at the right frequency.

More information at - www.jyetech.com

Friday, 25 November 2016

Retro CCTV monitor


This is the second of these little black and white televisions I've picked up. I think my wife got this one in a charity shop in Portaferry (for £3 if I remember right). They run on 12 volts or a load of batteries and have a radio as well as TV.



Anyway, a bit of Internet research revealed that all of the RF side of TV things is handled by a single chip and the composite video is dealt with by old-school transistors. This made it easy enough to cut into the video circuit at the right point and hook it up to the DVD player and we have a retro composite monitor.


The radio section was on its own board which I removed along with the speaker, front panel switches and so on. Some plastic card to fill the gaps, epoxy and satin black paint gave it a bit of 80s class! I also added a power LED to the front and re-wired the antenna jack socket to act as the video input.

The DVD player is actually a recorder I got on Freegle because the power supply had packed in. In this case the transformer had fried, maybe due to a shorted 'bad cap', so I replaced the whole power board with a similar one from another broken DVD player. A bit of drilling and soldering and it is working like new. It would make a great CCTV security recorder.

Sunday, 11 September 2016

TV sound and tablet prescription

Well, the Finilux TV is working a treat except for the sound which went to intermittent mode very quickly. As far as I know the TV hadn't been used in some time so it suddenly occurred to me today when I was out on my new (to me) bike I swapped for another TV (!) that the power amplifier in the TV might have capacitor issues the same as the power supply. I'll get a look at this during the week because this TV has a great picture and I want to use it with the YouView box I got from TalkTalk (which lay in its box for 2 years) to watch Wheeler Dealers on Quest. I need my fix of Edd and Mike.

My wee lad's Zoostorm tablet (Q6010) seems to have gone into limp mode, as in limp to the spares box. It has gotten locked into some sort of unresponsive state where the touchscreen isn't working and pressing the reset button or any of the Android reboot sequences does nothing. It was a strange tablet from the start, aimed at the education market and with a weird storage partition layout, but a quad core processor and a whopping 2Gb of RAM which 2 years ago was unheard of. And all for under a ton from CPC. The pity is that it runs Android 4.2.2 (JB) so could in theory be used as a Kodi box, but only if I can get it to work again. In the meantime, good dad that I am, he's getting my old Fujitsu M835. Back to paperback books for me then.

Friday, 26 August 2016

Rescued LCD TV - Bad Capacitors

I got this dead Finilux 32-inch LCD TV from Chris on Freegle. The power board was doing nothing, no voltages, so I took a good look at the capacitors and 6 of them were bulging and suspect. Raiding the spares box, I found replacements for all 6 capacitors and upped the voltage rating on 4 of them just to be on the safe side. Re-assembled the television and it is working like new.


Here it is running off a Raspberry Pi Kodi box via HDMI playing a music video on Vimeo. Picture quality is excellent.

Saturday, 23 January 2016

No-cost astronomy camera

Webcam from a broken laptop;
Short piece of 20 mm plastic pipe;
Cardboard jewellery box;
Old USB cable;
Hot glue gun.

Only thing missing has been a clear night sky!!

Tablet power supply upgrade

I was going to say 'repair', but really this is an upgrade. My son's Android tablet stopped charging and pretty quickly we tracked the problem to the power supply cable. This didn't surprise me because it was a pretty cheap bit of cable, speaker wire really and I always thought it wouldn't last. The tablet itself is a bit of an oddity, a Zoostorm educational tablet with 2gb RAM and a quad core processor, but it was being sold by CPC a year ago for under £100. The reason may be the odd OS customisation with a strange storage layout almost certainly set up for school use, but we have tackled that and Need For Speed runs just fine on the device!

I tried reusing the moulded DC plug, but it shorted out so a trip to Maplin got me a replacement for £2. It is the smallest plug in the range as it happens. Looking at the cable, I thought I might as well do the job right so a delve in the spare cables box turned up a nice heavy wire from a defunct power supply for something else. Once again heat shrink sleeve came to the rescue to make a strain relief for the plug and the join to the stump of the old cable at the power supply end, and make the whole thing look nice and neat.

Better than when it came out of the factory!

Tuesday, 27 October 2015

HDMI Converter Upgrade

One minor problem with working with the Raspeberry Pi is the lack of a VGA display output. I say minor because most of the time the Pi is being used with a TV with an HDMI input or in 'headless' mode where I am logging in from elsewhere on the network.

Over the years I have acquired a small number of LCD VGA displays and I have a couple of these in the workshop along with a 32-inch LCD TV I picked up. Being able to use one of these displays with the Raspberry Pi was always going to be handy so I needed an HDMI-to-VGA adapter. These aren't overly expensive (£15 will buy a good one from CPC), but always on the lookout for a bargain I purchased the one below on eBay for £2.50 (direct from China).

The problem is that the Raspberry Pi HDMI output has very limited current on the 5-volt line, not enough to successfully run the adapter. Also, the Pi checks the HDMI output very quickly for a display and the adapter needs time to boot up so being able to run it from a separate supply would be an advantage. The Pi can be programmed to lock to HDMI and also to delay in checking for a display, but I wanted to avoid that for the time being.

Cheap HDMI to VGA adapterThe adapter came apart very easily by simply prising the bezel out from around the VGA socket. The HDMI specification gave me pin 18 as the 5-volt line so I was able to identify that on my adapter this was a purple wire which went to a pad on the PCB marked '18' (Doh, but it is always a good idea to check!). An old lightweight USB cable did the job for power and after cutting the purple HDMI wire, I soldered the red USB wire in its place on the PCB and the black USB wire to a spare ground point. Interestingly this PCB had pads for both a micro-USB socket and a small DC power socket (maybe 1.7mm or so) so a more sophisticated upgrade would be possible.

I tested the set-up to check it was working and have now bored a hole and re-soldered the power cable to neaten the whole thing up. It looks pretty professional now and the picture quality on a Panasonic VGA monitor is excellent.

I'm thinking of buying another of these and hard-wiring it into another VGA monitor I have to give the monitor an HDMI input.