Monday, 22 May 2017

Back to the Dew Heater Controller

Well its been a funny old day, wonderful sunshine one moment, torrential rain the next. So during the rain, ive been hidden away in the workshop.

A project thats been awaiting further work is the Dew Heater Controller. Having picked up a box for it at the Blackpool rally, it was about time I cracked on with it!

The Dew Heater bands come with phono plugs on them, and as the temperature sensors can be operated in two wire mode, and the phono panel sockets come in red/black pairs, i'd already decided to use phonos for all the control connections

The DHT22 humidity sensor, which provides the environmental monitoring needed to establish the dewpoint values, was the first component to be installed, as it needed to go on the outside of the box. Held down with an M2.5 nut and bolt, its legs pass into the case via a row of 1mm holes. Once complete, these and the sensors base will be sealed

A 2.1mm DC Jack for the main 12V supply was fitted at the opposite end to the sensor. This is the right hand side (sensor on left). The three pairs of phono sockets then fit on what will become the 'top' or 'back' of the box, depending on how you think of it!

One of the most important tasks was to decide where all the various internal modules would fit! The photo below shows the three MOSFET driver modules, and the OLED displat module, placed where they would eventually reside

And after a lot of measuring, drilling, filing, checking, and remeasuring etc, the OLED can be seen fitted. Here it is under test with just the Arduino Nano controller

The arduino is mounted on a bit of Perfboard, and hot-melt glued into the corner. In this location it is still possible to easily connect a USB lead to power it for testing, and for later software upgrade if required. Ive used up a lot of left over ribbon cable that was just kicking about, so lots of coloured heat-shrink on the connections!

In this second to last photo, the majority of the work is done. All the modules are glued in place, each of the MOSFET drivers has been tested, using a temperature sensor tag soldered to the first input phono! (the TO92 package you can see).  All that remains is to complete wiring up the 2nd and 3rd sensor channels, the control outputs to the MOSFET modules, the 12V supply lines and the outputs to the three heater channels.

A final going over with a pencil eraser will be needed to clean up the front panel.

I also have a 40m CW transceiver, a JJJ Electronics v.1, on the bench belonging to Bob M1BBV.  He obtained this ready built but in unknown and unfinished condition from a Silent Key sale. Well, it at least works, after a fashion. Its a little unstable but should be fine once the board is cleaned up and reworked. A number of parts need to be properly seated. I'll post some pics of the work on that later.

Friday, 19 May 2017

Getting Started on the PRC-350 LiPo Pack

The 4S LiPo pack was received with a clear marking that it was shipped at 30% and should be brought to a storage charge level as soon as possible, so I decided to day to at the very least get the main connections sorted so I could do this.

The battery case originally had just a single tag for each connection, however as I want to add additional facilities to this build, I opted to use a pair for each terminal. A short length of figure 8 DC cable is attached to one side.

The main cables of the battery attach to the pair of tags on the other side. This is very heavy gauge wire and required a lot of heat! All connections are sleeved for insulation. In addition the screws will later be covered with hot melt glue to ensure there is nowhere to short out! Likewise, the inside of the alloy case will be lined with an insulating sheet.

With both main cables attached, I could put the battery on charge.

While this was charging to safe storage level, I started work on the cutouts in the battery case for the external balance connector, low voltage alarm module etc. The usual combination of drilling and filing required here, along with the usual stabbed fingers! First to be cut was the hole for the 9way D type connector that will serve as the external balance charging port, and the 'loop through' for the low voltage monitor.

The wiring involved isnt complex, but it is quite fiddly. Now, ive noticed some constructors seem to have a fear of heat-shrink! But, there really is no excuse for not sleeving connections properly - especially when they are attached to a device that can give several hundreds of amps short circuit current!

 I did choose however to remove the pins on the voltage monitor board and solder directly to it. One track was damaged to ive wired straight to the input resistors. Below shows the monitoring and balance charging wiring in place and under test on the battery. A 9-way D plug is wired for 'loop-through' connection, this plug will be attached when the battery is in use and the alarm and monitoring facility is required (or briefly when in storage to check the condition)

With the wiring done, all apart that is from the external balance charging cable, the D socket could be secured to the case. Ive provided a 2.1mm DC Jack socket for an external 15V output. This will have an internal fuse attached! The part cutout is the start of the 'window' for the monitor boards LED display. Not shown, as I dont have it yet, is the USB output, which will be wired from the same fuse via a switch. The switch mounting position I will decide later.

It is remarkably tricky tightening nuts and soldering wires at the bottom of a small closed tin!

Thursday, 18 May 2017

Lithium conversion for PRC-350

The PRC-350 is a 2W VHF FM manpack transceiver in the Clansman range. Its probably the most famous military radio that no one has ever heard of - because its the radio whose antenna has the flag attached in this photo -

The one in my collection has the common 'battery cassette' intended to take 10x NiCd 'C' cells. I have 8x Alkaline cells in mine at present, but that is an incredibly expensive way to run the set! Original, or NOS, NiCd battery packs for this radio seem to be unobtainable now.

A full set of modern 'C' size NiMH cells could be used, but this is rather expensive, and heavy. So for around the same cost, and having an empty, decelled alloy battery pack available, Ive decided also on this radio to go the Lithium Polymer route.

Its the shipping that makes your eyes water buying these things! But, give them credit at Hobbyking, i ordered yesterday afternoon and it was here first thing this morning!

I was aiming for a pack of around 1800mAh, which I thought more than adequate for the PRC-350, but then I saw this one on special offer - 2200mAh for just 30p more, but without a main output connector. Well, I would have had to cut the connector off anyway! So a good bit of extra capacity for a few pennies extra!

This is a 4S pack, giving an output of 14.8v. The PRC-350 has a 'nominal' supply voltage of 15v, but an operational voltage range of 12 to 21v, so this pack will be spot on. I will add a low voltage monitor and alarm of course, using D sub connectors as I did on the 24v 4000mAh pack for the PRC-320/PRC-351, the connector doubling as the balance charge port. I will also add a DC output connector to allow it to be used to supply other kit, perhaps also a USB charge output?

All being well, this and the PRC-350 could be going up for a SOTA on Snowdon in a couple of weeks!

Tuesday, 16 May 2017

More Spot on 10m

After yesterdays 'success' of a whole one station near Stuttgart spotting my QRPp 10m WSPR signal, im pleased to see that ive been spotted again in the last hour on 10m. This time by G3IGU near Doncaster - around 20 miles away! I suspect this is less to do with a change in propagation and more down to G3IGU turning on a 10m receiver!

Mobile Project Construction

Yesterday, I happened to know I would be sat waiting in the car for an hour, so I decided to take along something to do, other than my Kindle or trawling Facebook,

So I took along a handful of tools, a roll of solder, and a gas powered soldering iron, plus my 2nd Chinese Pixie-2 kit

In order not to set fire to the car, I took a wooden board to work on, with a few screws in to act as a stand for the iron!

The sockets, sounder and crystal socket I had already soldered in previously, so it was just all the small fiddly parts to do in the cramped confines of the drivers seat of a Ford Fiesta!

After a brief 25min soldering session, all but two components were installed. These two turned out to have been supplied the wrong values!

I quite enjoyed doing this, so plan to improve my little 'worktop' by putting a raised edge on it to keep parts from rolling off, and using the router to cut some shallow grooves to put loose components into.

Monday, 15 May 2017

DL4YHF CW Keyer Tamed!

With a half hour or so spare this evening, Ive collected up some tools and bits for a little 'out-of-workshop' project building, namely the 2nd Chinese Pixie-2 kit I had kicking about, but also had chance to add the modification resistors to the keyer

This is the 18k series resistor (making 19k with the 1k that is already on the board), and the 39k parallel resistor across the 100k potentiometer.

Well, I havent measured the speed range maximum and minimum yet, but by ear the minimum sounds like 5wpm, the maximum like 40 or 50wpm. And right in the middle of the range are the speeds I want!

I will rig the keyer up to some software later that can tell me the actual speeds, so I can make up a scale for the control. But it seems the mod has done the job.

10m WSPR hit!

Sometime over lunch, my WSPR U3S beacon was spotted by DF4UE near Stuttgart. Conditions on 10m at the moment are practically dead! So, thats not a bad result for around 150-200mW!

DL4YHF CW Keyer - Taming the speed control?

Ive had a quick chat with Wolfgang DL4YHF by email regarding the speed range of the keyer. As suspected, the speed control range cannot be easily changed in the code, so the best plan of attack is to modify the resistance range of the control.

Yesterday I measured the resistance at my preferred slowest speed (just before the control becomes unresponsive) as 47k, and that at my preferred maximum speed (probably about 45wpm) as 18k.

The fast speed is the easy part to deal with. By assuming the pot to be at zero, then its a case of replacing the 1k input series resistor with an 18k unit. But the slow limit is more difficult. The resistance difference range needed from the pot is 29k - of course no such pots exist.

Rather than replace the 100k pot that is in place, the answer is to parallel it with another fixed resistor to modify the range. In this case, a maximum value of 29k can be achieved by paralleling the potentiometer with a fixed resistor of 39k.

I will try this tonight and see if I get an acceptable control range. Replacing the 1k resistor would entail removing a number of wire connections to get the PCB out, so instead I will probably keep it in circuit and add the 18k in series with it. I doubt the extra 1k will make much difference to the speed range.

Saturday, 13 May 2017

Building the DL4YHF Keyer

Having got the DL4YHF PIC CW Keyer working on breadboard, the next step was of course to make it a permanent build. I had already decided on the box I wanted to use, a small beige plastic one i'd picked up somewhere, and decided to use perfboard and hard wire the circuit, rather than muck about trying to design a PCB or waste my stock of Veroboard.

My first task then, was to size a piece of perfboard to fit the box. To do this two rows of holes needed to be removed, and the sides filed, plus the corner cut-outs. This allowed the board to fit easily down in the bottom of the box. I also decided to use a socket for the PIC chip, but couldnt find any 18pin DIL sockets, so had to bodge one from a couple of the 14pin sockets ive loads of. But probably the most important task was to search my junk boxes to find a holder for a 3v coin cell! The one I found was surface mount, but a few spare PCB pins soon had it in place.

Of course, after the build was complete, and while looking for something else entirely, I happened to find a load of 18pin DIL sockets!
The wiring on the underside is all point to point, mostly using the legs of the components themselves.

 With all the components installed, I checked it fitted the box, then drew out the circuit from the board, to make sure I hadnt missed anything or got anything wrong. This is well worth doing, but only practical for small projects. In the event, I'd missed a critical connection - the Vss line to the PIC!

 The final underside wiring is shown below. Im quite pleased that I managed to find a layout that had all the components on one side, as that meant the board would fit as low in the box as possible, giving me more space to work with. At this point I connected the board up to the speed control pot using croc clip leads and tested the keyer to make sure it was working.

So next came the work on the box itself. I was making the layout up as I went along, and the case and controls layout was no exception. A lot of work with files was needed, as I wanted to add a slide switch to allow me to turn off the sidetone. I also had to be careful where the output connectors went so as not to short the battery!

The 3.5mm stereo jack socket for the key caused trouble. The cheap ones i'd got proved that you get what you pay for! The act of tightening it up caused the damn thing to distort out of alignment such that I couldnt get a plug in! It took me quite a while to figure this out and correct it!

So with the board in place and the wiring ready, I turned my attention to the top panel. Initially I thought I would have to leave the project only part finished as I could only find one panel mounting push button. But I then decided to use a pair of very nice looking but PCB mounting square tactile buttons. This meant a lot more file work to create the square cutouts!

The buttons themselves had to be secured with hot-melt glue - trouble is, ive run out! So, I searched the workshop, salvaging little bits here and there, until I had enough to secure the two buttons. The speed control pot is also secured using its anti-slip stud - this involved some very careful drilling of 1.5mm blind holes!

The filed cutouts are not the neatest but are reasonably square and with the buttons in place dont look too bad. The light blue caps of the buttons go nicely with the beige colour of the box.

The final component to fit was the LED, which is used by the chip to indicate various special states. Everything was then tested again, before finally screwing up the box and adding a control knob.

And here it is, connected to my Hi-Mound paddles. The volume level of the sidetone is rather low, even with the sound holes drilled in the side, but its adequate.

I now need to build the cables to connect it to my radios! The speed range is a bit wide for my purposes, but thats something to sort out at a later date. Ive found a spot which gives around 8-12wpm, which is where I want it.

Friday, 12 May 2017

10m WSPR today, wonder if i'll get any spots?

Put the U3S on 10m WSPR this morning. So far, not one spot. This of course is not unexpected, but hopefully there might be a little bit of Es at some time. Just one spot of my 200mW would be nice!