Category Archives: Other

Blog, Other

Vigo Tec VG-A4 Writer/Engraver

I wanted to a cheap XY plotter to try some experiments and after looking at ebay I saw an inexpensive plotter to try, the Vigotec VG-A4

Construction was fairly easy, although the only instructions that came with the package were in Chinese. I have since found the instructions here Although due to translation issues, they are not much more help.

The Plotter was constructed and worked first time as a writer using the example JPG’s and the VigoTec Writer Software. (Downloadable here )

Be careful about belt tightness. If the belt it too tight you will easily loose position when moving. Otherwise the hardware is well made an designed.

I haven’t yet tried the Engraver software as this involved changing the firmware in the driver board.

All working well, I started to try driving the plotter by G-Code. There is of course Zero Documentation.

So after a lot of trying things I found the PenUP/Pen Down commands which are M03 and M05 respectively. You will need a delay for the pen server to do its thing, Im currently using G4 P1000 to give a 1 second delay.

This mostly works, as a test I put in a move G1 X Y Z and a pen down followed by a pen up. I did this 4 times to create a dot in each corner of a square, The pen only responded to two of them, I have no idea why.

The Writing software is very buggy. With many of the adjustments not working at all. I also find that you MUST do a pen down then a pen reset before using G-Code otherwise the pen wont work at all. (The pen UP button appears to do nothing. Unless you have loaded an image).

Be careful using G0 the plotter appears to lose position even with the lightest of pens. To cure this and especially if you are using anything heavier, use a G1 X Y Z FXXXX to set the feed rate. ( When using G-Code the speed slider is ignored)

There are some issues with G1 and pen up/down, but I haven’t fully discovered what the causes to these are or any solutions yet.

Microprocessors, Other

Micro Python with ESP8266 & Oled Display

How to load a test script

After loading python on your own system

Install esptool
pip install esptool –upgrade

Install AMPY
pip install adafruit-ampy

Download ssd1306.py from https://github.com/adafruit/micropython-adafruit-ssd1306/blob/master/ssd1306.py

Plug in the board and find the Com port that is created (mine was COM4)

Download the micropython from https://micropython.org/download#esp8266
Should save as a bin file like esp8266-20171101-v1.9.3.bin

Erase the board
python esptool.py –port COM4 erase_flash

Flash the board with MicroPython
python esptool.py –port COM4 write_flash –flash_size=detect -fm dio 0 esp8266-20171101-v1.9.3.bin

Bodge the ampy package

Open /usr/local/lib/python2.7/site-packages/ampy/pyboard.py. Find line 171. Specifically go to the enter_raw_repl method:

add a time.sleep(2). So it becomes
def enter_raw_repl(self):
self.serial.write(b’\r\x03\x03′) # ctrl-C twice: interrupt any running program

# flush input (without relying on serial.flushInput())
n = self.serial.inWaiting()
while n > 0:
self.serial.read(n)
n = self.serial.inWaiting()
time.sleep(2)

Create main.py

Using a terminal open the com port and at the >>> prompt write

f = open(“main.py”, “w”)
f.write(“print(\”main.py: Hello\”)\n”)
f.close()

Write the oled Library to the board

ampy –port COM4 –baud 115200 put ssd1306.py

Create a file called oledtest.py with the following content

import machine, ssd1306
i2c = machine.I2C(scl=machine.Pin(4), sda=machine.Pin(5))
oled = ssd1306.SSD1306_I2C(128, 64, i2c)
oled.fill(0)
oled.text(‘MicroPython on’, 0, 0)
oled.text(‘an ESP8266 with an’, 0, 10)
oled.text(‘attached SSD1306’, 0, 20)
oled.text(‘OLED display’, 0, 30)
oled.show()

ampy –port COM4 –baud 115200 run oledtest.py

Blog, Other, Wimshurst

Flashing light prize 2017

Details for the entry for the 2017 flashing light prize.

The Flashing Light Prize  is an informal & fun contest to find the most unusual way of flashing an incandescent light bulb.

So, being me, it had to include high voltage, and It had to use what I had lying around as I’ve been quite short of time recently.

My Wimshurst came to mind, but I wasn’t sure the two laden jars would hold enough energy to light a lamp. A quick test proved that as long as I was using small lamps, there was plenty of power available.

My initial tests failed, as the leads from the bulb made a point source that leaked charge away from the Wimshurst, so it never charged up to enough voltage. This was an easy fix, I attached a 1/2″ brass ball onto the bulb leads, with a 12mm Gap I go a flash rate of ~1Hz and ~40,000V, plenty for a 6v bulb 🙂

I had a few 6V 30ma Grain of wheat bulbs and these flashed really well from the sparks from the Wimshurst. The problem was after about 4 flashes that only just lit the bulb the filament would explode and leave a small arc lamp behind.

My thought was that the thermal shock from having 40,000V dumped into the filaments (rather than 6v) was probably something to do with the failure. I started to look around for a large HV inductance that would limit the inrush.

An Ignition coil secondary was put in series with the bulb and then I had a second thought, use it as a transformer to power the bulb at lower voltages.

So two bulbs were connected across the Ignition coil primary and the secondary was put via a spark gap across the Wimshurst terminals.  This flashed really reliably.  Power and speed could be varied with the spark gap, although at full separation the bulbs looked excessively bright so the rate was kept quite small.
2017 flashing light entry video

 

Wimshurst machine details/build

 

Incredibly, I won with this entry … So Chuffed !

Can’t wait until September to defend the title …

https://www.flashinglightprize.com/ 

Flashing light challenge 2017 my second entry

Other

Perpetual Motion

In the Royal institution’s museum there is a perpetual motion machine (used towards the end of this video  )

It occurred to me that this piece of equipment is over 100 years old and over that time it has regularly been used to demonstrate the futility of perpetual motion.

So it has been running, although intermittently, quite consistently for over 150 years, powered purely by presenters and demonstrators demonstrating that it doesn’t continue to run.

It’s therefore powered purely by the fact that it is a perpetual motion machine, and no doubt will continue to do so for hundreds more years.

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Blog, Other, Other teslathons

Mini Maker Fair Derby

Come and Meet Extreme Electronics and the Twin PI tesla coils (and some other stuff 🙂 at Derby Mini Maker faire. We will be by the jet engine just off the main hall.

[gview file=”http://www.extremeelectronics.co.uk/wp-content/uploads/2016/10/Maker-Faire-2016-poster.pdf”]

Blog, Other

Lichtenburg figures for the BBC One Show

Ok so it started as one of those phone calls that asks if I can make safe sparks. Quite a regular ask for me and I always start with no. High voltage isn’t safe.

Anyway after a number of discussions. I was asked to make a “relatively” safe way of allowing a BBC presenter to create lichtenburg figures.

The method I came up with was to use a 15KV OBIT (Oil Burner Ignition Transformer). I prefer this type of transformer to a MOT (Microwave Oven Transformer) for purely safety reasons. One touch from an MOT and you are either Burnt, Dead or Burnt and Dead, Not good odds. This is due to them giving up to 100mA at 2KV, plenty to get 1-2mA across the heart of the unwary. The other issue with MOT’s is they are low enough voltage not to cause corona, which means they are silent, a dangerous mix. OBITS on the other hand give out 10-15Kv at 5-10mA. Not safe, but you are much more likely to survive an accidental contact.  Also due to the OBITs high voltage, you can hear when they are on.

The Control.

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The boxes were split in to two, the Transformer and high voltage at the “HOT” end and the lower voltage (mains) at the other.

The control box had a key lockout which needed to be in place for the HV to be turned on. This key was attached to me with a short lead so I could ensure the HV area was safe before I allowed any power to the box. The Go button was momentary, so that if any danger was spotted the power could be quickly removed.

The HV end was in a roped off area (out of shot)

The mains was supplied via an earth leakage trip for added safety.

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The HV end was supplied via 30KV insulated cable to two crock clips that attached to the screws on the board.

The board was dampened with water and washing up liquid, (required to properly soak more than just the surface of the board)

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This really is a don’t try it at home experiment, when the power is on, you can’t touch ANYTHING, damp wood, water and high voltage  not a good mix.

Luckily the presenter was Marty Jopson a HV fan so the explanation and safety briefing was fairly easy as he understood the risks. (He has his own collection of HV equipment including a one Tesla.)

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This was all done in the most glamorous of locations 🙂

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The result. No one died… and I think they got a good film of the Lichtenburg figures being produced.  I will find out 19:00 BBC1 4th July 2016.

Other Making Lichtenburg links

Lichtenburg figures with toner

Lichtenburg figures over water

Lichtenburg figures in wood.

 

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Other, Uncategorized

Lichtenburg figure test

Test of transformer choice and wood type for reliable Lichtenberg figures.

Obit – 20Kv 20mA

Both pieces of wood lightly soaked in water (only) just before test.

wood – 4mm MDF

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Wood length 18″ – each pattern ~6″ across.

 

Course grained 3 ply

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Burns only continued in line with the grain. Test abandoned.

 

Blog, Other

Capacitance of a human body

by Paul E. Schoen of P S Technology, Inc.

There is some more information [regarding the resistance of a human body] at http://van.physics.uiuc.edu/qa/listing.php?id=6793 , where it states that the external human body resistance is about 1k to 100k Ohms, and the internal resistance is 300 to 1000 ohms. Only a thin layer of dry skin separates the internal resistance from an external object.

The human body capacitance to a far ground is 100-200 pF, which is really a minimum value. This correlates to an impedance of about 13 megohms at 60 Hz, which corresponds to a minimum of 9 uA at 120 VAC to ground. This is enough to be sensed and used for capacitively operated light dimmers.

Here is a way to measure your body capacitance: http://web.mit.edu/Edgerton/www/Capacitance.html

The inside of your body can be considered a conductor, and thus if you place your hand flat on a metal plate, you will form a capacitor with an area of perhaps 15 square inches, with a thin (maybe 0.005”) insulating layer of dry skin, which will form a capacitor much higher in value than the 200 pF stated above. According to a formula in http://www.sayedsaad.com/fundmental/11_Capacitance.htm , this would be C = 0.2249 * k * A / d = 1350 pF, (assuming k for skin is 2, about like dry paper). This will be an impedance of about 2 megohms , and current of 60 uA. This is still below the normal threshold of sensation, and still far below the usual safe current levels of 1 to 5 mA.

The actual thickness of the epidermis (per http://dermatology.about.com/cs/skinanatomy/a/anatomy.htm ) varies from 0.05 mm (0.002”) for eyelids to 1.5 mm (0.06”) for palms and soles, but the actual outer layer of the epidermis that is a good insulator is composed of flat, dead cells, which is much thinner. So the capacitance could be much higher than the quick estimate above.

Probably the main reason for electrical current to reach levels high enough for electrocution to occur (6 to 200 mA for 3 seconds, according to http://www.codecheck.com/ecution.htm ), is when skin becomes sweaty or otherwise loses its dry protective layer, which quickly exposes the underlying 1000 ohms or less, which will conduct 120 mA at 120 VAC.

There are safe ways to measure the body’s resistance and capacitance using realistic higher voltages, skin conditions, and contact surfaces, but I’m not going to suggest anyone try it. Suffice it to say that ohmmeter readings are misleading, and any carelessness around any kind of voltage source can be dangerous.

For very high voltages, there are standard minimum distances that must be maintained between a worker and an energized line: http://www.dir.ca.gov/oshsb/rubberglove.html . I found this on a search for rubber glove testing.

The field intensity near high voltage lines is so great that it might be fatal to touch them even if you were suspended in free air. You may notice that birds can sit on lower voltage transmission lines which are 5kV to 50 kV or so, but not on 200kV+ lines.