Bugger - Always read the small print!

 Ordered the U10 MCP9801 temperature sensor IC for my mcHF transceiver. Arrived today, fair enough it was only coming from the next big town across, but still pretty quick all things considered. So, I thought i'd solder it in tonight.

Its at this point I realise that the chip ive ordered, is not the 8-SOIC SMD unit that fits the boards and that is just about within my soldering capability - but a damn 8MSOP package, otherwise known as a fleck of muck with legs.

OK, so it is the same device electrically, but theres no way im ever going to be able to fit the thing! So, the correct 8-SOIC unit is now ordered, at a few pence more cost, from the exact same supplier. Probably not even worth the hassle of trying to send it back!

mcHF Build Progress

 Ive not done much updating on this project, but it is coming along.

I now have the LPF toroids wound and installed, going by the specified number of turns. There is a lot of info out there about these, and much of it seems contradictory. No matter, i'll see how the transmit performs per band and if needed will adjust these coils later.

One problem I had was how to mount the static discharge neon lamp. I didnt like the idea that some had used of milling out the shielding plate and putting it on the 'wrong' side of the board, but also wanted the BNC rather than SMA RF connection. So, I carefully cut away some of the plastic body of the BNC in order to be able to solder the neon bulb in place.

As luck would have it, I discovered that the supplied enameled wire is self-fluxing, which makes it a lot easier to do a reliable joint.

Another trick ive used is to solder the nuts onto the tabs of the TO-220 power transistors and regulators. This makes them captive, and so removes a very tricky step in trying to hold the nut, and transistor, in alignment with a hole inside the case, while the screws are inserted!

And, so far, this below is my progress. All the sockets, switches, encoders, the LEDs, TFT display, latching relays, and LPF toroids are fitted. I decided to solder the display direct. Hopefully that doesnt turn out to be a mistake later!

 I still have the transformers to wind, the VSWR bridge to build, and the power semiconductors to install. I intend installing the temperature sensor for the oscillator, thats on order and should be here in a few days. A small bridge of copper will link it to the oscillator package for best temperature monitoring. I also dont wish to remove metal from the shielding plate, so one of the 220uF 16V SMT electrolytics will have to be replaced, ideally if I can find one on a surplus board or in my SMD stock, with an equivalent in the little square tantalum packages.

Ive already had the ferrite cores out of the bag and given them a good going over with a sanding block to remove any sharp edges, which are notorious for cutting into the enameled wire and causing shorted turns. I also need to look at and if required make the modification to the wiring on the PCB for the VSWR bridge, where I believe one of the windings is connected in the wrong place. This is a design flaw but should be simple to correct.

So far, apart from the lack of a fixed, standard build manual for the version, ive only noticed one gripe - it doesnt have enough LPF and BPF sections! Meaning its lower frequency limit is about 2MHz without excessive harmonics. I appreciate its designed to be very compact, but we have access to 10 amateur bands, so just 4 sets of filters is insufficient really.  5 or 6 sets of filters would have been much better, in my opinion.

Either way though, im looking forward to being in a position to try it out!

Toms 2nd Clock Project

 After the success of Toms first little Chinese clock kit, this week we moved on to the second. This is the SH-E 879 kit. A somewhat bigger PCB than the last one, 6 digits, and battery back-up, plus an on-board 5V regulator.

We spread the build over several days, tying it in to his home schooling. Each part of the build including me explaining what the component is and does, and why. Starting as always, with the least heat sensitive parts. We had a slight problem when one of the oscillator load capacitors pushed its PCB pad up, so that section of track had to be linked out.

Tom knows that I insist on a specific orientation of parts to ensure component values can be easily read. He managed to put two resistors in the wrong way, but electrically this doesnt matter so ive let him off!

And so today, he completed the build, I checked the soldering for dry joints, missing joints, jumps and splashes. All looked good.

And - it didnt work!

We spent ages trying to find anything amiss. In the end, Tom left me to fault find. After quite some time, I discovered that one out of the four 3mm LEDs, actually fits the opposite way to all the others! After changing this around, and repairing the now broken track that it connected to, I had the four LEDs lit. But still no clock function! The microcontroller Vcc pin voltage was correct, the ground pin had continuity to ground, all the bus pins showed expected voltages, even the clock pins looked right! I was about to break out the 'scope, when I thought to check how the chips reset line operated. It turns out reset on this is active high, rather than low as is usual. So for the processor to run, the reset line should be low, which it was. The microcontroller was in fact the only component that Tom didnt install - I fitted it due to the risk of bending the pins...

...I decided to pull the chip - oh, bugger! Guess which one and only leg had got bent under? Yep, the bloody reset pin!

So now, after fixing my own cock-up, its working. We havent yet played with the one and only button to find out how to set it. Two things im unhappy with though - 1, for some reason there is a 10k resistor over the diode that feeds the back-up battery onto the Vcc rail, this looks like some sort of charging attempt, but the coin cell is non-rechargeable. I wasnt going to fit this resistor, and only did so just in case I was missing something in the fault finding! I'll likely remove it later. And 2, the four 3mm LEDs are far too bright! They are current limited by a 470 ohm resistor, I think maybe 1k or so would be more sensible, and reduce the current draw a little as well.

But on the whole, another successful kit build by Tom.

RH Electronics Arduino Geiger Counter - Testing

 A few notes on this kit. I had hoped that it might be operable at 3V, but a test of this showed it doesnt. The LCD backlight works, and the unit generates a series of three bleeps as if starting, but there is no display. There is HV to the G-M tube, so it looks like its maybe just on the edge. Perhaps 3xAA to provide a 4.5V supply would work.

Anyway, I found out a USB power bank that was actually charged, and connected it up. To do so I had to piggyback the Geiger Counter onto the power terminals of a little digital clock kit that the power bank was connected to. But the kit powered up successfully, displayed its start up splash message, and went to work.

I have connected it up to my spare BOI-33 G-M tube using 1/4inch fuse clips. This is equivalent to the perennial SBM-20 tube.  My test source is  my trusty old WW2 radium faced pocket watch. The kits red led lights at a count rate above 50 CPS (counts per second), while the blue one flashes for each detected pulse. The top button when held switches between CPS and the bargraph display, and the uSv/h (microsieverts per hour) and CPM (counts per minute) display. The bottom button mutes/unmutes the sounder.

Two video clips show both display modes in action.

So, what next? Well, decide on a case for it, decide which tube (s) to build into the case, how to switch between them, what battery supply to provide (this means testing the 4.5v 3xAA or 3xAAA option, and possibly doing the 78L05 mod), what sort of connector to use for the interface output (9-way D type? Or 3.5mm stereo jack?) and what connector to use for an external probe. I probably wont put a switch for the HV voltage, as all my tubes work on 400V except one, and this kit cant provide the 1.6kV for that one!

On the whole, its been a pleasant build, and its a nice little kit. I would say its a tad overpriced, and the lack of an on-board regulator is a poor oversight. Suggested improvements for the manufacturer -  Add an on-board regulator, make the component pitch fit better (maybe it needs a couple of extra mm of board space!), include the proper battery connector, and move to a Molex type connection for the HV rather than the screw terminal, and add a brightness control preset for the LCD. Oh, and add an option to display the PWM values and measured HV voltage.

Update! - Ive had chance to test using a 4.5V supply. Rigged up with 3x AA cells in a 4x AA holder (one place shorted out with a croc clip jumper), the Geiger Counter works flawlessly. Depending on the current drawn, most of which will be for the LCD back-light (so modifying it to have a variable resistor to set the brightness is sensible) i have no doubt it will also work perfectly well on 3x AAA, which is not only a heck of a lot cheaper than a PP3, but easy enough to fit in a case.

Testing again with 3V, the issue is not with the counter itself, which by the flickering LED and rapid clicking, works fine at 3V (the ATMEGA328 microcontroller can go down to 1.8V) but with the HD44780 LCD driver ICs, which need more than 3.3V to run.

RH Electronics Arduino Geiger Counter - Build

 With not being at work today, only supervising my youngests home schooling, and needing something to relax me and take my mind off other worries, Ive had time to build the RH Electronics Geiger kit.

I will discuss a few issues ive found with it in due course.

The first task was to solder the connections between the main board and the LCD board. To do this, I decided which side to put the pins on, put the connectors together, sandwiched them between the two PCBs, fastened the boards together with the pair of stand-offs supplied, and soldered them in. This meant that I could then remove the screws, and separate the two boards, with the connectors now in perfect alignment. Note that there are four unused pads on the LCD board, and three pads below on the main board - dont connect these together!

Now, with the boards separated and the LCD safely back in the box, the resistors were installed. Here I found the first bugbear - the spacing between the holes is very tight with the size resistors supplied. This wasnt a big problem with the low voltage side, but the HV 10Mohm resistors are even bigger, and had to be installed as you can see in the photo below. Ive 'zig-zagged' the measurement chain resistors to help them fit more neatly and to offset the nearby bare metal leads.

While fitting the resistors another pet hate came to show itself - most of the silk-screen part numbers get covered up by the components! There is a layout diagram available to download, but I still personally dont like it. Also, why the diagonal parts? I can only think that this was done for some aesthetic rather than electrical reason!

Next up were the right-angled header pins, which allow for 5V supply connection and the TTL interface lines, and also the 400/500V selection jumper. Along with those, the IC DIL socket, push buttons, and clock crystal were fitted at this stage.

With the build coming along nicely, time for the ceramic capacitors. Here I found that the pitch of the holes on the PCB was much smaller than the pitch of the preformed leads on most of the supplied capacitors! All but the two 22pF for the crystal required their leads reforming to fit, an annoying and fiddly task that shouldnt have been necessary if the correct pitch parts had been supplied.

And with the ceramics fitted, next went in the electrolytics (note that the polarity symbol on the PCB is tiny!) and the inductor. The inductor needs its leads bending at a right angle so that it can lay flush to the board, as shown.

At this point - i stopped for lunch! (beans and sausages on toast, if anyones interested).

So, after lunch, the semiconductors were installed. Three transistors and three diodes. One of the transistors is a high voltage MPSA44 which drives the inductor to generate a high voltage pulse, which is then multiplied by the diodes. Here also, it was found that the pitch was insufficient for the diodes to be mounted flush, and so these are also positioned vertically.

Almost done! The two LEDs, one red, one blue, but both unlabelled and clear cases! Luckily my multimeters diode test function is capable of lighting LEDs, otherwise I would have had to find out my LED tester! I decided to mount these a little proud of the board. The buzzer and the screw terminal for the G-M tube connection went on next, and then finally the high voltage capacitors.

After a careful inspection of the board and my solder work, I decided I was happy with it and would now insert the microcontroller. Several rounds of check and recheck here to be absolutely certain it went in the right way around, and that no pins got bent under.

Now, there is space and pads for a battery connector, but no pins or socket supplied. So one was found out from my stock of components. Its a bit of a tight fit, such that it couldnt be disconnected with the LCD board fitted.

Here though is my big disappointment with the design - there are ample connections for ground and 5V on the header pins, so why have a 'battery' connection? 5V batteries are not exactly common! There is ample space on the board, and in fact already suitable filtering and bypass capacitors, for a 78L05 regulator to have been built in! That would have made the 'battery' connection a much more practical 7 to 30V battery input! (I wouldnt recommend running one at 30V though, it will get rather warm! But a 9V PP3 or a 12V supply would have been great for the sake of a single extra TO92 package!). I will probably make this a modification once the unit has been thoroughly tested.

Another modification i may make, is to make up a ribbon cable for the LCD. As it is, the unit is small but chunky, which might make fitting it into a suitable case for portable use tricky. Likewise, when in a case, the LEDs will have to be moved off board. The buttons of course can just be paralleled with a pair chassis mounted.

Because the G-M tube connection is by a screw terminal, whose screws are hidden under the LCD board, I have only carried out a basic functionality test so far.

 Details of testing and results will be in the next post!

RH Electronics Arduino Geiger Counter

 Feeling a little flush (this being before I was suddenly hit with an expensive DEFRA poultry housing order!) and really not liking doing my own coding, I decided i'd give the RH Electronics Arduino IDE Geiger Counter kit a try. ( https://rhelectronics.net/store/arduino-ide-geiger-counter-dosimeter-diy-kit-with-lcd.html ).

I placed the order for this on the 10th of December. Coming from Isreal, the package arrived on the 4th January.

The shipping label clearly shows that it was dispatched on the 12th, so considering the Christmas period and all the other disruption to postal services at the moment, I dont think thats bad going.

Inside the box, which was well sealed, the kit itself was securely shrouded in bubble wrap, and although there are no detailed instructions for the build, the included schematic is clear and relatively easy to understand. Its perhaps not a beginners kit as it stands, as putting it together does require a reasonable knowledge of the components and how to read the schematic.

The actual electronics package of the kit consists of the LCD module in its own wrapping, and all the other parts in a small self-seal bag. There is hardware supplied for mounting the LCD. Not supplied is a G-M tube or mounting hardware for it. A G-M tube could easily double the cost of the kit! The LEDs and buttons are PCB mounted - these will have to be reworked when the unit is fitted into a case. 

The circuit also runs on 5V and there is no on-board regulator. Personally I think this is a bad oversight by the designer, and a low drop out 5V regulator should have been included. I will see if the unit will run reliably on 3-4.5V (2 or 3 AA cells), if not then I will modify it with a 5V regulator for a 9V PP3 battery.

The circuit uses a clever PWM HT generator driven by and feedback monitored from the ATMEGA328 microcontroller, but otherwise the G-M electronics are pretty standard. All the clever stuff is done in software. LEDs and a buzzer are included for the traditional 'geiger counter' feel, and it is capable of driving 400v and 500v tubes with just a jumper change. This will work with all my tubes except the alpha tube, which requires 1600v. A header is provided for serial comms to other devices.

I plan on including a socket to connect an external tube (probably my huge STS-6), as well as the internal one(s).  With a suitable switch, I plan on installing a standard SBM-20 tube and the tiny SI-19 tube within the case.