Mk2 Theremin Build

Originally, about a year ago, I was commissioned to build a Theremin for a colleague. He paid me sufficient funds to obtain the necessary electronic components, and away I went to build a version of the Moog Etherwave.

Which wouldnt work. I can see now the likely reason, which is that the originally specified and now very hard to obtain inductors will have different self resonances than the more modern devices I used.

Anyway, rather than persevere with this design, I noticed a much easier to align version in one of the copies of Everyday & Practical Electronics that Steve G7TAO has given me. So, having found a supplier for the necessary IF transformers, and obtained a PCB from the publisher, im now well on the way with this build

A few other parts I dont have in stock, so have to order in, including very annoyingly a 7809 9v regulator, which I was sure I would have had! Most parts I have either as new stock or salvage. Some I can even salvage from the abortive Etherwave build. It is now effectively costing me money to complete the project, but in a way I dont mind, as id very much like to see not only a completed working machine, but also Daz's attempts to play it! And of course, I did promise to build him a working Theremin!

Clansman PRC-351 Antenna Connector

The Clansman PRC-351 VHF manpack is designed to be used with a 1.2m whip antenna, for which it has a special multi-angle antenna connector. Unfortunately, on my set, this is badly worn, such that the antenna will not stay up in position, but can overcome the position indents under its own weight and fall down.

It occurred to me that it might be possible to repair this internally, so today I removed it from the radio to open it up and take a look.

The above photo shows the dismantled antenna connector. The main boss uses a pair of plastic inserts that are pressed into the notches on the body by a semicircular spring clip. These inserts were worn almost flat on the face towards the body.

Turning them around and reinserting them, at first glance it looks like it will be a good repair. Next job was to brush out all the dirt, dust and powdered plastic insert!

With the connector cleaned, I reassembled it, and replaced it in position on the radio. A further task for the future will be to either replace or repair the antenna contact in the radio which is rather loose.  Reassembling the connector was a simple reversal process, making sure not to loose the little O ring or the two washers. If I was going for a full CES rebuild, then I would have followed the old soldiers adage of 'always grease your ring' when replacing the two O ring seals.

Sadly, after refitting the connector to the radio, it was found that the antenna will still drop from position if knocked or shaken too much. It is tighter than it was, but not sufficient to use the whip antenna with the radio on the back. Luckily, PTSNorfolk stock these connectors, so ive ordered a couple of replacements.

Two packages have just arrived, which despite their small size seemed to give the postman trouble getting through the letter box! One is the PCB for the EPE Theremin, which im building on behalf of a work colleague. The other is an Arduino Uno board, and a 'getting started' book, courtesy of Steve G7TAO, for Sam to use to learn more programming techniques. As Sam has a friend over to play today, im going to have a bit of a read!

Clansman PRC-351 modifications

This morning I decided the -351 VHF manpack needed its first on-air testing under controlled conditions. So, with me operating the FM1100, I kitted Sam out with the radio. But, I also insisted he looked the part, so stuck my 95 pattern smock and my beret on him! Its always worth, as a parent, acquiring a good set of  embarrassing 'ransom' photos!

So with Sam on the -351, and me on the FM1100, we compared performance in both W (whisper) and L (Loud) modes.

In L mode the Tx from the Clansman is too low, and the Rx audio too high. In W the Tx mod is perfect, but the audio in the headphones is too low. It seems to be a good amateur set, a bit of modification will be required, to 'cross over' these settings such that at least one of them has good audio out and good Tx mod. This should really be quite easy, perhaps just a case of adjusting the deviation and the audio levels.

Yaesu FT-290Rmk1 fault found

 Well, after all the testing, it turns out to be a common 'stock' fault, albeit showing itself in an unusual guise.
The external power socket on these is notorious for its internal switch contacts sticking and causing the external power to be fed onto the internal batteries. But in this instance, the contacts were shorting out the internal batteries when the set was switched on. Im not sure how exactly, but 'exercising' the contacts (by plugging the external power lead in and waggling it about) has solved the problem. It remains to be decided whether or not i'll replace the socket.

So, here she is, complete with leatherette carry case and shoulder strap, and rubber duck antenna -

Another FT-290Rmk1

Many thanks to my old friend and colleague Steve G7TAO, who has donated to me his Mk1 Yaesu FT-290.

Not only does this radio have a few of the ancillary items mine doesnt, it also doesnt have the USB carrier balance fault mine has! allowing me to get back on 2m SSB whilst mine is 'in the shop'. But it does have one odd issue

The radio works perfectly on external power, but not on batteries. On batteries, switching the set on shorts the pack, but also the pack never reads above 10v! This is despite the batteries being perfectly fine used in my set! Whats more odd, is that after briefly switching on and then off, I can watch, on my meter, the voltage work its way back up slowly! The power input socket seems to be good. Im starting to suspect something strange like one of the protection diodes is at fault.

Mobile USB power

I have a dashcam DVR. Its mounted, as the law requires, behind the rear view mirror, at the passenger side, and not impinging on the area swept by the wipers too far. Its set to start recording automatically as soon as its powered, which up until today was when I pushed the USB adapter into the fag lighter socket. This arrangement is far from ideal, not least because the power cable just hangs about loose.

So today, I installed a 12v to 5v 3A USB power converter, using a clever little gizmo that allows you to add an extra fused connection into the vehicle fusebox by replacing a fuse with this device. I chose to pinch a connection from the front windscreen wiper supply, which I knew was an ignition switched circuit. This is a 20A mini blade fuse. So, pulling that fuse and installing it instead in the lower socket of the 'Add-a-circuit' fuseholder, a 5A mini blade fuse in the upper socket, and plugging the whole assembly into the original fuses place in the fusebox, and I had a 5A switched 12v supply.

The microUSB power cable to the cam was fed up and under the headliner behind the courtesy light, across to the passenger side door pillar, down inside the trim, and behind the glove box - which happens to be where the fusebox is. The DC converter blocks +ve wire was crimped to the new fuse units output wire, and the -ve, fitted with an eyelet crimp, bolted to the chassis metalwork.

Now, this power block came with a standard USB socket as its output connection. So, a section of the outer jacket of the cable was removed, exposing the two wire cores, to which the USB lead for the cam, now cut and with the cores bared back, was attached using two 'snap-in' insulation displacement connectors. I was a bit dubious that these would work with such thin wire, but on powering up all is well. The camera starts up when I start the ignition, and shuts down when I kill the engine.

The original USB connector - well, using a Stanley knife I cut out a slot in the plastic of the fascia between the glovebox and the central column of the dash, and now have a switched 5v USB port for charging my phone or Kindle!

Following on from yesterdays work on the Clansman LiPo battery, all that remains is to mark it up in such a way as to make it obvious its not a standard battery and must not be charged on a normal charger.

So, here it is swathed in masking tape ready for spraying. Whilst purchasing the automotive parts for the job discussed above, I also picked up a can of scarlet red spray paint. The top cover of the battery is going to be sprayed red, along with a one inch wide stripe right the way around the battery case.

Clansman Lithium Polymer battery conversion finished

With the Zippy 4000mAh 7s 28v Lithium Polymer battery, the charging port, the low voltage alarm module and the temperature sensor all already installed into the alloy case, all that was left for me to do today was pack the remaining space with foam, and attache the lid.

Rather than glue nuts to the inside of the lid, at the risk of them coming loose and at worst case shorting the battery, I used impact adhesive to secure a pair of softwood runners inside the alloy lid. Into these, through the fixing holes, ive put in eight small woodscrews. I would have preferred small domeheads to the countersink heads these have, but they will do.

All that remains now is to add the several bright red or yellow safety warnings! Its absolutely essential that this is not confused for a NiCd pack - if charged improperly, this is essentially a neatly packaged incendiary bomb! Charged properly and handled correctly, its a damn sight lighter to carry than the NiCd beside it in the picture!

The NiCd pack weighs 3.4kg. The LiPo pack weighs 1.12kg.

Put that into perspective when walking the hills with the PRC-320 - the weight difference is 2 1/3 liters more water!

Another slice of PI

Prompted to get off my arse and do some work by a fellow detectorists progress on his Surf PI, Ive spent some time today getting the project a little further on.

The first task was to piece and drill the holes for the controls, and to create the hole pattern for the speaker. One of the controls (the sensitivity) has a bit too long a shaft but i'll decide whether or not to cut that down at a later date. The loudspeaker is not yet secured, there will be a layer of mylar film between it and the holes. The speaker holes are all 2mm, which will help against most splashes.

With the batteries installed and the coil connected above. Ive used twin shielded loudspeaker cable, which I just happen to have lots of.Only one core is used, giving a spare should the cable be damaged. This extra length of 'floating' copper doesnt seem to have any detrimental effect.

The test bed setup is shown below. In this configuration it 'see's' a small jubilee clip at about six inches, and a small pair of long nose pliers at around 8inch. Oddly it doesnt detect at all a two inch long phosphor bronze heatsink retaining clip! Must remember to try that against the Ace 250!

The final photo here shows the unit fully boxed . The next job, once the speaker is secured, will be to build a shaft and mountings. Once thats done, I can decide on a coil housing and a final coil.

Spectrum/Alpha 4160c LED message board

Im sure you've all seen them, those scrolling LED message displays in shops and offices. Well, I have one, seemingly in working order other than a big chunk knocked off of the end of the case (I have the chunk so thats an easy repair!), acquired from scrap.

But I have a problem. I dont have the correct firmware version to allow me to actually interface to it and make it work! So the hunt is on to find the firmware. The manufacturer wants an extortionate price for an EPROM, so that route is out. At present then im looking at the possibility of reverse engineering it to bypass the built in computer. This would mean a drastic loss of capability, but then just how many ways do you really need an LED sign to scroll, fade, etc?

The EPROM is a 27C1001, which is a 1Mbit (128k x 8) device, so clearly the firmware file for this machine is pretty hefty!

The actual sign is made up of five boards (one of which has the computer piggy-backed to it), each containing the driver capabilities for two rows of five 8x8 bicolour LED matrix units. The driver electronics look to be pretty standard - hex buffer/driver logic, and shift registers.

Heres one of the boards, ive had this one out whilst I metered out the LED matrix pin-outs -

Im not overly impressed I have to say with the power connection in the middle of the board! A proper high current low voltage bus would have been a much better idea!

If I can find a way to get this working, then it will be available for use by the Lions club for any events etc where it would be useful.

Further on with the Surf PI

Its been quite a while since I worked on the Surf PI metal detector. But, this new year my resolution is to get projects completed!

Before I can work on a proper waterproofed coil, the main electronics need boxing up. It turns out the PCB fits nicely into an ABS case I had bought for another project but not used. This leaves a LOT of free space, enough for the 3x Lithium cells and the loudspeaker. It wont be properly waterproof, but should survive splashes ok.

The battery holder has been secured with impact adhesive, actually a spray on type from Screwfix. The two controls will mount on the top panel, and as can be seen the 4-way avionics type connector for the coil cable is on the bottom panel.

The lid of the box will serve to provide a mounting point onto whatever I decide to use for a shaft.