Friday 27 July 2012

Review: Skytronics / Mercury 600.219 Multimeter

I needed a new cheapo multimeter, and bought this off of eBay for a grand total of £18.90 delivered. That's about "30 bucks" to everyone else. I couldn't find a review, or even a decent photo beforehand - so I thought I'd put this here for any future people looking for info on the "Skytronics" (mine arrived branded as Mercury, so who knows) model 600.219 "professional" digital multimeter. Here's the official website:
Here's the packaging. Nothing fancy, but looks alright:

The case - hmmm, looks and feels cheap. Plus they put an extra space in "Digital", so it looks like DIGIT AL MULTIMETER. Keeps everything tidy though. Press stud fastening.
Inside the case - everything very nicely shrinkwrapped. Manual printed on toilet paper, but in English rather than Chinglish.
Test leads/probes - Brilliant! Really! They feel nice, have a decent quality cable on them, came with protective end caps that fit well over the nicely sharp tips. Leads are properly rated and marked. Strain relief where the probe meets the cable. Can't fault them.
The meter itself - Good points: measures almost anything, a lot more than most cheap meters. Seperate sockets for A/mA/V to prevent oopsies. The screen is great, very clear. The stand is good. Meter could do with some little rubber feet to stop it sliding around on a flat surface.

Bad points: the dial! Ugh, it has the worst click in the world, very springy. Unfused 10A range - assuming some idiot decided to try and measure "how many amps are in the mains", rather than blowing the non-existant fuse, the meter would likely just explode and blow your arm off.

The yellow protector case thing is a bit useless. It makes it a lot bulkier, and a lot harder to get the stand out of its slot in the back.
Interesting point 1 - internal temperature sensor. Plugging the thermocouple in (via the included mini-K to banana adapter) auto switches to using that rather than the internal sensor.
Inside the meter - 2 boards. Smaller one backs on to the dial it seems. Soldering is neat. No bodge wires or loose components. 2 small glass fuses for the V/mA ranges, no other input protection. The battery is a pain to get in and out, there is a seperate door for it behind 2 screws, but its slightly too narrow to get a PP3 and the plastic clip through without a firm push. I didn't bother unscrewing the rest of it, I thought the springy click wheel might fall apart or something.
Interesting point 2 - the manual on/off switch is a proper switch that the battery goes directly to. This means the current draw when off is zero. Current when on is around 4.9mA, so you could hope for around 100 hours runtime on one battery.

In conclusion, a good cheap meter with a lot more features than one costing a tenner. Worth the little bit extra in my opinion. Great value for money.

I wouldn't recommend it to any "real" electronics professional, or anyone working on mains electrics - but then again, I'd hope those kinds of people already have high quality gear, and not Chinese crap from eBay!

Friday 13 July 2012

Raspberry Pi PS2 - Part 2

So I eventually ordered another hub after finding out the Pi has issues with lots of 'powered' hubs. My selection process was eBay, sort by Price (lowest first) and then choosing the one with sockets on cables for ease of desoldering. This cost me about £2. You can also drink this apparently as it is "easily potable"
Apart from the Chinglish, the description on the back is also completely wrong - it states that it includes a mini usb cable and user manual, and can provide 500mA/port - yeah right.
Whoa, smallest hub ever! I was expecting to have to unscrew it, but it literally fell apart in my hands.

I thought I better test it before I went any further
 This one worked first time...
Wires came off easily enough. I labelled the board afterwards, to save confusion when re-soldering it

Testing with an externally powered hard disk through the hub

Picked it up OK after I realised unlike every other USB device in the world, whoever designed this hub chose to cable it in the order VCC, USB+, USB-, GND
Glueing the usb ports in to the case. I had to shave a tiny bit of plastic from the connector to get it to fit next to the screw hole

That bit of PCB was getting in my way, so I cut it off. It didn't look important.
 Sockets and LAN mount glue drying. Exciting stuff...
 Wouldn't know it had changed :)
Same with the ethernet socket. That's an 8mm spacer underneath it by the way

All parts in place. I'm still waiting on a panel mount power socket, which is why that is still hanging out of the back

Lid back on, and final testing. Still no idea what I'm going to do with it though...

Saturday 7 July 2012

Raspberry Pi PS2 - Part 1

After not being imaginative enough to think of anything useful to do with my Raspberry Pi, I decided to put it in a case with a few other bits to make a semi-useful mini PC. The target? Slimline PS2 I got off eBay for 7 quid (faulty laser). I've always liked the slim PS2 case. I'd have bought a brand new housing kit instead, but I couldn't find one in black. DX were (and still are) out of stock (item 29213). Anyway, it was a bit scuffed but would do the job.

I wanted rid of the disgusting sticker on the back, but as it turns out, Sony do a better job of making stickers than they do lasers. It wouldn't peel off.

The trick seems to be a syringe of isopropanol and careful scraping with something softer than the PS2 plastics - I used an iTunes giftcard.

The isopropanol didn't instantly dissolve the glue like it does with other stuff, so who knows, maybe water or soap or something would have worked instead. Who cares.


The finished result I was happy with though, no nasty sticky marks left at all.
Opening it up, I was quite surprised that the entire innards come out in one chunk. There's a screw tucked away between the controller ports that's easily missed *ahem*.

I bought a drive enclosure to tear apart, the rest of the stuff I had lying around

One thing I did notice when mentally planning this, was that none of the microusb cables (even my genuine Nokia one that came with a phone) would power the R-Pi properly. Testing between TP1 and TP2 I was lucky to get 4.25v! I ripped the end off of one of them and unsuprisingly, they're made from pretty much a few atoms of metal twisted together. That's a 3mm LED for size comparison. Plan B - ignore the microusb and go for power through GPIO.

The drive enclosure I bought cost about £2.50 delivered. It's the cheapest one I could find, which presumably was designed by a 5 year old as they used USB A on the device *sigh*. That "illegal" cable went straight in the bin. I should have sold it on, see if I could have got some idiot to try and network 3 computers together with it or something.

I lied before, I did buy one more thing. This useless adapter! I mean really, what purpose does this thing serve? I know, I bought one intentionally, but surely nobody else buys them. It's a HDMI male to female adapter for anybody that didn't guess. Read that again; yep, male to female adapter... as in socket on one side, plug on the other. It makes as much sense to me as the USB A to A cable above. Well anyway, I'm glad they do exist, as I needed one for this.

Cheapo unbranded USB hub. Check out the wonky diodes! I figured it'd be a lot easier deconstructing one with sockets on wires rather than PCB mounted sockets. I was right.
This has to be the most shoddy product I've ever taken apart. It really looks like it was soldered together by some 6 year old kid using a Bic lighter. I'm amazed it works...
I want to keep my R-Pi mod-free for now (waited for years for this one, don't want to destroy it!) - so I left the A plug on the hub, to go straight into the Pi
They "helpfully" labelled the connector on the hard drive enclosure board just in case I wasn't too sure. That board was just glued in to the enclosure. The USB A socket was easy enough to desolder - they hadn't even bothered soldering the casing down, it was just held by the 4 pins.
This made my job easier - I found that the PS2's usb holes were a perfect match for the sockets I salvaged from the hub!
See - exact fit! The thickness of the plastic USB port cover is a perfect spacer to line up with the hole in the case.
Deciding where to put stuff. See what I needed that M-F HDMI adapter for now? I'll dremel a hole for it and glue it in later. Same for the SD card... er... without the glue.
Removing a PCB mounted ethernet jack cleanly was a bit of a pain tbh. Best technique I found was add solder in a big blob covering all 8 pins, then heat the lot and pry it loose. I'm open to suggestions for better methods. I tried solder braid and it just wouldnt remove every spot.
Can you guess what that 8mm thick square of plastic is for? Anyway, 10/100 only needs 2 pairs. Green and Orange.
O/W - 1
O - 2
G/W - 3
G - 6
Well there's one part that works fine!
For the USB (data) cabling I went with 0.25mm Kynar in blue and red (it's all I had).

For power, I used scraps of cable from an ATX PSU. Overkill, but again, best I could find laying around.
Time for a quick test. Here's where things start to go downhill...

Firstly, the bunch of cable you see top left I guess is too thin internally - 4.4 or so between TP1 and 2. I'll deal with that later, so I croc clipped directly on in the mean time.
Everything looked happy enough IRL
But then... sadface.jpg
The Pi didn't like the USB drive. Had I destroyed something? Broken the USB Hub? Hmmm...
For the record, this is currently drawing 0.83A idle. It seemed about right.
I quickly desoldered the USB data lines from the hard disk, and it seemed OK with just the hub.
OK, maybe its the drive controller. After all, it must have cost about $0.05 to manufacture. I soldered one of the original USB sockets back on to try a flash drive in. Plug the drive in, the Pi reboots! Fail again. Got to be a faulty hub, right?

I should add, although the pic doesn't show here, I did try and power the hub though the DC jack in case the R-Pi couldn't handle it on its own - made no difference at all.
I had a spare hub the same as the previous one. Check out the wonky diodes again! They've got a little solder slug trail this time.
What a mess. But still, I tested it in a real PC and it does function properly...
...but not on the Pi. That's with zero hardware mods, just the Pi and the hub with a drive plugged in.
 Targus hub from my laptop bag... straight away. Two dodgy hubs, right?
 First hub, in a real PC...


Well, I guess I'll have to buy some more USB hubs and hope the Pi "likes" them.
 be continued.