Projects completed while Home Isolating (HIP) - March 2020 onwards

The 2020 Covid-19 lock-down is a very worrying time. Many of us are struggling with income.
I have been exploring ways of expanding my on-line workshops and activtites but on the plus side,
I have had time to finish all sorts of projects and explore new ones. Here is a page of projects completed while 'home isolating'.
Note: most of these projects have been made over a two to four day period, doing about 2 hours a day.

click here for my 'X-files' page (other 'interesting' projects / ideas)

stepper motor controller

Stepper Motor I experiments:
UCN5804 unipolar stepper motor controller (for 5, 6 or 8 wire motors) - 19th - 22nd March

basic circuit taken from here

... which is a lot neater than this test set-up (below) ...

stepper motor controller wiring

70 MHz transverter

10 watt 70MHz transverter (28 MHz to 70 MHz) - 24th to 25th March
The left hand pcb is the main transverter pcb while the right hand pcb is an attenuator board with relay switching circuits.
These are pcbs I purchased on e-bay (I didnt design or make them) but I wired them up and designed my own aluminium box layout.
Transverter store web page

70 MHz 5/8 wave vertical

1/2 wave vertical antenna for 70Mhz band with π-network matching circuit, with four 1/8th wave radials - 13th Feb & 26th March
(Note: this one is only used on 10 watt)

10 GHz gun-diode transmitter

A 10GHz gun-diode transmitter (ca. 1990's style) - 27th March
This circuit is based on the one found on page / section 9.45 of G. R. Gessop's VHF / UHF handbook (RSGB ISBN 0 9006 12 63 0).
I built the pcb almost a year ago but had left all the other bits on my 'to make' shelf, only now had the time to drill the box and complete the project.
(Note: I think there is an error on the original circuit diagram - the speech amplifer op-amp positive supply should go to the 12V line, not the potential divider)

LF helical antenna

1/4 wave 80m helical antenna (20m of wire wrapped around a 15m long fibreglass mast) - 30th March
The lowest end of the wire goes straight into my ATU and earth system.
(I dont have room in my small back yard for guy wires so the mast has to be supported at the base (see right hand photo)

pre-amplifer for Heil mic

pre-amplifier for Heil GM-4 microphone - 31st March
This mic preamplifier circuit is from p. 22 of R. A. Penfold's great little book - "Preamplifier and filter circuits", 1991, ISBN 0 85934-254-9.
I had made the pre-amp so I could use an old refurbished Heil GM-4 mic through my amateur radio transmitters.
Although this particular circuit sounded great through an amplifier / headphones it failed to work well through a transmitter (maybe impedance matching problems?).
After a year packed away I re-purposed it now for my on-line science workshops (e.g. for Skype, Discord, Zoom etc.) where it works very well.
As well as a push-to-talk button, I can also lock the pre-amp ON when its used for video conferencing.

hand bleeper

8 piezo bleeper hand-held alarm - 2nd April
I made this about 10 years ago, I had an illness that left my voice weak. I was teaching at the time and my voice was not strong
enough to attract the attention of kids in my workshops when they were all getting on with activities - 8 piezo bleepers got their attention !
Here I have re-purposed it for the Thursday night "Thank you NHS" clap - its better than banging pots and pans and I can also send 'Thanks' in Morse code !


IC706 MKII ACC Socket break-out board - 2nd April
I made up this break-out-board so I can get to some of the useful inputs and outputs on the 13 pin ACC socket on the back of my IC706 MKII amateur radio transceiver.
In particular I am shortly going to use the push-to-talk (PTT) outputs for the 'antenna switch' I am currently making.
(Note: extra / spare wire in pin 14 place) IC706 MKII Instruction Manual PDF (see page 6 for ACC wiring)

Anycube 3D printer

Anycubic i3 Mega-S 3D printer - 3nd April
My first 3D printer (Rep Rap Ormerod) is now about 10 years old and although it still working (its been repaired many, many times) it is time to up-date it with a new printer (to run along side it and perhaps replace it).
I ordered an Anycubic i3 Mega-S in Dec 2019 but it only arrive last week. It is sold as a kit, but really its a very easy build as it is basically
just two parts that need bolting together along with a few multiway connectors that need plugging in.
After setting up the printer and aligning the printed bed on my bench, I printed out my first object - two owls - (the 3D file came with the printer software).

3D printed Peak intrument holder

3D printed Peak Instrument holder - 5 April
Peak Electronic Design Ltd make excellent little component testers. A free 3D printed desk-top stand for the instruments is available
on the SOTABEAMS web site. It prints out in two parts and with the addition of just four self tap screws,
it assembles into a neat little stand. I am indebted to Roger (M0TJK) for showing me this page:
Sotabeams 3D stand for peak instuments/

Antenna change over unit

Antenna change-over unit - 5 to 7th April
This is a unit that auto-switches my transciever from the main antenna on transmit to a loop antenna (low noise) on receive.
I started this about two years ago; drilling the case, fitting the sockets, leds and switch but it had migrated to my 'to-do-shelf'.
I finally made the control pcb and wired it all up. The ACC break-out-board completed for the IC706 allows me to use the PTT line to
control the change-over unit nicely, however the RF activated mode still needs a bit more work.

70 MHz 1/2 wave and 5/8 wave verticals

1/2 & 5/8th wave vertical antenna for 70Mhz band with π-network matching circuit (with four 1/8th wave radials) (Note: this one is only used on 10 watt) - 14th April
I swapped the bee-hive trimmers for better variable caps (ca. 60pf air spaced) and arranged them so that I could easily change the inductor as well. Here are two photos:
left is the half wave (2m high) vertical with π-network matching unit components below and
(right) the 5/8th wave (2.5m high) vertical with π-network matching unit components below it.
So far it seems that in use they both perform about the same.

Antenna change over unit

low power 12V power supply bus - 15th April
This is a very simple way of connecting up to four 12V devices to my power supply.
The connections are not high power so only really useful for low power devices such as pre-selectors, audio filters, relay chage over unit etc.


IC706 MKII ACC Socket break-out board MKII - 15th April
See above for detail (2nd April). I wasnt happy with the ribbon cable in the MKI, as it was not screened.
I brought a screened 13 pin DIN lead on e-bay, cut-off the inline socket and wired the wires to the pins of the break-out-board.
IC706 MKII Instruction Manual PDF (see page 6 for ACC wiring)



SOTABEAMS LASERBEAM-VARI digital audio filter - 15-17th April
I was given the SOTABEAMS module about four years ago and only now have had the time to build it into a digital audio filter unit.
I also built the 10 watt audio amplifier to drive a loudspeaker(s).
You could make the unit much smaller than my one shown here, but I wanted it to fit on my shelf in the case shown here to match other equipment.
The SOTABEAMS module is very impressive, easy and intuitive to use.
SOTABEAMS web site

Collapsed retina eye operation Sussex Eye Hospital - 19-21st April
I started to lose sight in my right eye on the 18th April and by 19th the Sussex Eye Hospital took me in - they were amazing.
I had some complications (due to an accident I had 40 years ago) but overall the op went well:
i) removed original gel in the eye, ii) laser & thermo 'stapled' the retina back, iii) add liquid to eye and then iv) inject a C2F6 (Hexafluoroethane) gas bubble. Then had to lie on my front for threee days.
The C2F6 bubble will diffuse out over a month or so, but is put in so that when I lie on my front it rises to the back of the eye and holds the retina in place while the body knits it back in place - like a gentle 'helping hand'.
Back home on 22nd. Amazingly during, and after the op, I have had no pain at all, a slighly sore eye of course, but no real pain - the NHS are amazing !

salt celler base & 3 guy wire clamp

Some 3D printing - 26-27th April
As I can't do anything very physical for a while I can enjoy making things with my 3D printer. Left photo: a base for our salt cellar - to catch salt crystals that tend to litter the table top.
Right photos: a guy cable attachment clamp for 3 guys to go on one of the upper sections of my fibre glass mast. The device is made from two identical 3D printed parts, brought together around the fibre mast.
A bolt secures the two together on one side, while the other uses a guy cable / rope knot (if need be, both can be secured using rope). The green cord is for illustrative purposes to show the idea ...
I also printed this out for M0TJK Enclosure for SOTABEAMS filter kit

rot encoder drives stepper motor

Stepper Motor II experiments:
Rotary encoder directly controls stepper motor (no PIC needed) - 28th April to 1st May
I have been commissioned by Whitgift School to build another physics demonstration and this circuit will be useful to control the postion of mirrors in an optical demo.
This circuit takes the quadrature o/p's from a rotary encoder to drive the (bipolar) stepper motor coils directly (using a ULN2003 buffer).
No PIC or clever switching circuits are needed as the rotary encoder is doing all the 'clever' stuff.
circuit based on that shown here (

1/12 wave coaxial transformer

1/12 wave coaxial transformer: a 75 ohm to 50 ohm converter - 3rd May
I have some very good quality 75 ohm coax cable that I will be using on a 4m dual dipole antenna (more details below soon).
Here I will be phasing up the two crossed dipole to get various polarisations using switchable coax phasing lines.
Now feeding a 50 ohm system with 75 ohm should only create a 1.5:1 VSWR, if there is no reactance present.
But some reactance (and additional resistance) may creep in via the matching / phasing circuits - in which case this circuit will help.

PIC control pcb for BPF

PIC control board for SV1AFN band pass filter unit - 6th May
I am using a PIC16F877 to control a SV1AFN BPF unit (more details soon). It's rather 'over the top' to use this PIC to control such a simple circuit
but I happen to have a batch of them and it also means I can use a very powerful PIC BASIC complier, which makes development really easy.
The other board on the right is a 5V PSU board which also has space for the RS232 unit required for in-circuit bootloader programming.

4m band crossed dipoles

4m band crossed dipole phaser circuit

Experimental 4m band crossed-dipole & phasing unit - 1st - 13th May
I built a set of crossed dipoles (45 degree and 135 degree) for the 10m band but 'plugged' in elements for the 4m band.
These are wired using high quality pair of 75 ohm cables into a phasing switch unit.
By switching in various lengths of 1/4, 1/2 and 3/4 wave sections I can get: 45 degree slope, 135 degree slope, vertical, horizontal and left and right circular polarisations.
Everything is done at 75 ohm (using 50 ohm quarter wave sections to transform the two 'parellel' dipoles back to 75 ohm.)
As its hard to get perfect phasing harness lengths and perfect switching, I kept everything at 75 ohm and then used the 1/12 wave transformer (above) to make 50 ohm.
The bench-test shown here uses two 75 ohm dummy loads (purple) but early tests show the system also works with the dipoles.
(Phasing circuit from VHF-UHF handbook, 2nd Ed. 2013 Ed. Andy Barter, ISBN 9 781905086313 page 158)

3D printed 4m band crossed dipoles center

3D printed center holder for light weight 4m band crossed-dipole - 16th - 21st May
The crossed-dipole set-up for 4m band shown in the 1st-13 May entry was a modified 10m band anttena and was simply too heavy to go on top of my fibreglass mast.
So I 3D printed a X-piece to take small aluminium rods that cam hold 1m long Al welding rods for the dipole elements.
The result is something much, much lighter than the original. VSWR on the set-up very good, less than 1.5:1 on all polarisations.
Note: the 'old' 10m band baluns (coiled coax) are still in place.

4m band crossed dipoles with 1 to 1 baluns

Light weight 3D printed 4m band crossed-dipole with 1:1 baluns - 27th - 28th May
I replaced the 'coiled coax' baluns (that were made for a 10m band version of the antenna) with 1:1 coax baluns based on the I0QM web page.
The VSWR on the output of the phase switch set-up is very good, less than 1.5:1 on all polarisations.
I0QM 1:1 balun web page / PDF

Stepper Motor III

Stepper Motor III experiments:
Bi-polar motor driver - ca. 30th May - 16th June
This version uses the DRV8825 bi-polar stepper motor driver to control a standard bi-polar motor (often used on 3D printers etc.)
You can buy very cheap ready populated pcbs on e-bay and I just made up a 555 pulse circuit to drive it.
At first the unit would not work but once I added the +5V and 0V rail to the board swich inputs everything came alive.
(Note: the board DRV8825 needs at last 12V to reliably drive the stepper motor)

aluminium U

U-Aluminium for experiment 'boxs' 9th June
Its expensive and a bit of a waste to use nice new boxs for my prototype experiments so I decided to buy some
1m lengths of U-channel aluminium extrusions (1m x 4cm x 8cm) from e-bay and cut them into convenient sized 'box's.

FT817 push on knob

3D printed extension knob for FT817 - 10 -11th June
I have been experimenting with push on knobs to go over the small tuning knob on the FT817 transceiver.
This one has an arm that allows for fast tuning. I will add more details of this to my 3D printing page asap
CSC 3D printing web page

7 element 2m yagi

7 element 2m yagi 3D printed parts

3D printed element holders for I0QM 7 element 2m band yagi - 3rd to 17th June
I made up an I0QM 7 element 2m band yagi about 4 years ago and found it worked really well,
but my version used a wooden boom (which I have used many times before for 2m band yagis) but I found the SWR went high when it rained.
So I built an aluminium boom version and used 3D printed parts to hold the elements.
It will be interesting to see if the SWR now changes when wet and also the electrical logevity of the 3D printed parts.
I used a 2m band 1:1 balun to feed the central dipole, as described above (27-28th May).
I0QM 7 ele 2m band yagi PDF

Proskit magnifier holder

3D printed holder for Proskit magnifier - 24th June
The Proskit magnifier is a very useful tool for electronics (as well as removing splinters etc.). It also has powerful white and UV illumination LEDs.
If you do get splinter it often feels like you need three hands:
one to hold the magnifier, one to use a tweezer to remove the splinter and the other the hand with the splinter to remove !
So I made up a 3D printed device to hold the handle of the magnifier onto a solid metal base (that I already had).

.... More ideas coming soon include: capacitance hat for helical LF antenna (?),
op-amp Analogue Computers, Energy Harvesting unit, switched capacitor laboratory pre-amplifier,
HF 5/8 wave vertical with coax-matching circuit, using a LMC6041 cmos op-amp to measure Circadian Rhythms, ...

click here for my 'X-files' page (other 'interesting' projects / ideas)


Dr Jonathan Hare, The University of Sussex
Brighton, East Sussex. BN1 9QJ.

home | diary | whats on | CSC summary | latest news