Projects completed during Covid lockdown (March 2020 till 20th April 2021)
The 2020 Covid-19 lock-down has been a very worrying time and many of us are also struggling with income.I have been exploring ways of expanding my on-line workshops 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 I experiments:
UCN5804 unipolar stepper motor controller (for 5, 6 or 8 wire motors) - 19th - 22nd March 2020
basic circuit taken from here
... which is a lot neater than this test set-up (below) ...
10 watt 70MHz transverter (28 MHz to 70 MHz) - 24th to 25th March 2020
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
1/2 wave vertical antenna for 70MHz band with π-network matching circuit, with four 1/8th wave radials - 13th Feb & 26th March 2020
(Note: this one is only used on 10 watt)
A 10GHz gun-diode transmitter (ca. 1990's style) - 27th March 2020
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)
1/4 wave 80m helical antenna (20m of wire wrapped around a 15m long fibreglass mast) - 30th March 2020
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-amplifier for Heil GM-4 microphone - 31st March 2020
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.
8 piezo bleeper hand-held alarm - 2nd April 2020
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 2020
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)
Anycubic i3 Mega-S 3D printer - 3nd April 2020
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 Instrument holder - 5 April 2020
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 - 5 to 7th April 2020
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.
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 2020
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.
low power 12V power supply bus - 15th April 2020
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 2020
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 2020
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 2020
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 !
Some 3D printing - 26 - 27th April 2020
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
Stepper Motor II experiments:
Rotary encoder directly controls stepper motor (no PIC needed) - 28th April to 1st May 2020
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 (www.instructables.com)
1/12 wave coaxial transformer: a 75 ohm to 50 ohm converter - 3rd May 2020
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 board for SV1AFN band pass filter unit - 6th May 2020
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.
Experimental 4m band crossed-dipole & phasing unit - 1st - 13th May 2020
I built a set of crossed dipoles (45 degree and 135 degree) for the 10m band for some experiments in the past. Here I have 'plugged' in elements for the 4m band.
These are wired using high quality twin 75 ohm cable 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 'parallel' dipoles back to 75 ohm.)
As its hard to get perfect phasing harness lengths and perfect switching, I decided to keep everything at 75 ohm but use the 1/12th wave transformer (see above) to convert it back to 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 center holder for light weight 4m band crossed-dipole - 16th - 21st May 2020
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 can hold 1m long Al welding rods for the dipole elements.
The result is something much lighter than the original. VSWR on the set-up very good, less than 1.5:1 on all polarisations.
Note: the 'old' (coiled coax) baluns / chokes are still shown in place in this photo.
Light weight 3D printed 4m band crossed-dipole with 1:1 baluns - 27th - 28th May 2020
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 experiments:
Bi-polar motor driver - ca. 30th May - 16th June 2020
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)
U-Aluminium for experiment 'boxs' 9th June 2020
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.
3D printed extension knob for FT817 - 10 - 11th June 2020
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
3D printed element holders for I0QM 7 element 2m band yagi - 3rd to 17th June 2020
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
3D printed holder for Proskit magnifier - 24th June 2020
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).
Experiments with Dallas chips - Aug 2020
I have used PICs to send RS232, I2C and SPI data to transducers but this time I am experimenting with the one-wire Dallas system. I am using the 18B20 temperature transducer and having fun extracting the C degree data from the more than 8 bit data sent back from the chip and show the data to 0.5 C resolution on a LCD display. My plan is to set up a data logger that I can take to the Alps and leave it there at ca. 2000m asl for a year ...
Elektor Data Logger Delux - 2020
I brought this data logger as an Elektor kit many years ago and lock-down has given me the chance to actually build it and mount the unit into a slopping holder.
3D printed obliquity of the ecliptic protractor - Aug 2020
I am exploring ways to use my 3D printer for Physics and Astronomy projects. This one is basically a 360 degree protractor (sextant) made in four 3D printed parts. It will be used to measure the altitude of the Sun over the year. From these measurments students should be able to determine the angle of tilt of the axis of the Earth reference to the plane of the Solar system - the so called obliquity of the ecliptic - and the latitude of the location the measurements have been made at. I have also 3D printed a verniar dial to read to 0.1 degree.
Outside yard steps - 9th Aug 2020
After 12 years outside my old steps have finally rotten away so I used this surplus wood to make up some new ones.
Rain cover for I0QM 7 ele - 11th Aug 2020
I have been having problems with the SWR of my IQ0M 7 ele Yagi going high when it gets wet. So I 3D printed a rain cover to go over the feedpoint, shown before the fixing nuts have been attached. Even though the feedpoint has been painted with selant the extra area covered by the cover seems to have solved the poor SWR issues - which is v good news.
50 MHz ARRL yagi - 11 Aug 2020
I have been building up the parts for the 3 element 50 MHz yagi described in the ARRl handbook.
Today I try it out on the mast and set up the hairpin matching section and adjust the dipole lengths to get a good SWR across the SSB part of the band.
Hall effect device - Aug 2020
Last year I built an instrumentational amplifier for physics experiments such as Hall effect measurments etc.
The Hall coefficent for copper is quite small but should be measurable for thin layers such as pcb foils.
This prototype should allow me to make some first investigations (ideally I would like the very thinest pcb foils but cant currently find an econimical source).
low noise current source for Hall effect measurements - 24th Aug 2020
The Cu Hall effect device mentioned above needs a stable low noise current source to drive it.
The Hall voltage being dependant directly on the current flowing through the foil.
So this is a simple battery powered current source. Its also useful for testing LEDS :-)
Vacuum system - 28 Aug and 4th Oct 2020
I was lucky to be involved in the discovery of C60 Buckminsterfullerene. Thin films of C60 are a semi conductor and elecrical devices can be fabricated from them. C60 sublimes thin films at high temperatures but this needs to be done at good vacuum. So I have been setting up a vacuum system (rotary pump + diffusion pump) over the last few years - all made out of surplus parts. Its taken me years as I have had set backs with vacuum parts and pressure gauges that have either been too expensive to allow progress or difficult to aquire the parts I needed. But I carry on when parts come up or given enough time I can work out a solution etc. Here I built a new stand to take the diffusion pump so I can take the experiments further.
BNC antenna - receiver patch panel - 21 Oct 2020
Fed up with cables everywhere and the awkwardness of re-wiring receive antennas with my receivers I built a patch board of BNC sockets that allows me to connect any of my receivers to any of my receive antennas, thers are, Receivers: R600, IRC7000 ICR70, homemade direct conversion Rx for 80 and two spares. Rx Antennas: LZ1AQ loop, VLF loop, MSF antenna, Datong active antenna, E-field active antenna and a 10 GHz satellite dish. BNC to BNC patch leads route through all signals via the front panel.
SV1AFN DC Rx BPF - 6th Nov 2020
I brought a simple two coil Band Pass Filter for 80m band from SV1AFN for my DC Rx. Works well
Whitgift PSD - Nov - Dec 2020
