Saturday, 20 May 2017

Southend Raspberry Jam 11

Today I travelled down to Southend on Sea to attend my first Southend Raspberry Jam, unfortunately this involved leaving home at some unreasonable hour on a Saturday.  The Jam was held at the The Hive Enterprise Centre (formerly the old central library).   

There were plenty of cool show and tell projects to look at,  some workshops and interesting talks.

I took some 
I took the Mega:bit and Micro Simon along I spent most of my time talking to people about my projects, however I did manage to have a look at the other projects on show.

My projects on display.


FabLab Essex had lots of interesting 3D printed / laser cut examples on display.


Barry Byford with his cool microbit powered big button game on show.


Neil Lambeth with his awesome football robots.


Nevil Hunt with his zbit:connect projects on show. 


A nice prize winning PiWars robot.


Some rather cool Raspberry Pi projects on show.


Some more pictures can be found on my Flickr page.   

Wednesday, 3 May 2017

14th Egham Raspberry Jam

On Sunday 30th April I travelled down Egham to attend the 14th Egham Raspberry Jam, it's my third time I have attended this particular jam. It was held at the Gartner UK HQ offices, which was easy to find and had plenty of parking. There were plenty of cool show and tell projects to look at, but no workshops or talks.

I took some awesome Boldport club projects and a colour mixing Raspberry Pi project along.  I spent most of my time talking to people about my projects, however I did manage to have a look at the other projects on show.

Some of my projects on display.

A collection of awesome Boldport Club projects.   


My colour mixing Raspberry Pi project.


A nice collection of Zbit boards from Nevil Hunt.


A couple of Raspberry Pi powered robots.


A nice collection of projects made by David Sweeney.


 Musical Octopus, using the awesome Makey Makey board.


Matt Sendorek's Raspberry Pi controlled Maplin robot arm.


Some more pictures can be found on my Flickr Page.

Tuesday, 2 May 2017

Commodore 1541 Disk Drive Repair

I recently acquired a classic Commodore 1541 disk drive.  It was in good condition, powered on and came with the original transit card (sometimes called a ”head vibration protector”).   


When it arrived I opened it up to have a peek inside. There is a large PCB which contains a MOS 6502 microprocessor, 2x MOS 6522 Versatile Interface Adapter (VIA) IC’s, rom, ram and various glue logic. I gave it a quick clean and powered the drive on, no magic smoke escaped. The drive powered up normally but the spindle motor didn’t appear to be running hmmmm.


Luckily there is plenty of technical information about these drives available on the web. Here are a couple of useful websites.

Bo Zimmerman's Commodore 1541 disk drive information

Ray Carlsen's Commodore 1541 disk drive repair information

I started checking voltages, the +5v supply was ok but the +12v supply was missing. This could be caused by an overload due to a shorted tantalum capacitor (C15) which sits across the +12V rail. I replaced the capacitor but this made no difference, it would appear that the +12v regulator (LM340KC-12) was dead.

These voltage regulators come in a TO-3 style package but I didn’t have any of these in my component stocks, so I had a quick hunt on eBay for some replacements.  A few days later the voltage regulators turned up so I set about replacing the faulty one. After I fitted the new voltage regulator I checked the voltage rails, both the +5v and +12v were now present.  

I powered the drive on, the green LED came on and stayed on, the red activity LED came on and the spindle motor ran for about two seconds then the red LED went out and the spindle motor stopped.  Good news I could now test the drive.


Next step testing the drive:

I hooked up the disk drive to my VIC20 and gave it a whirl, well that proved to be fruitless.  I tried to format a disk which started well, the red activity LED came on, the drive spindle motor was spinning and the head started to move across the disk. The format failed as the head stopped moving across the disk, the red activity LED started to flash (which indicates an error) but there were no error messages on the screen.   

Format failures can be caused by a write protect (disk tab on), drive door open, bad disk, bad or clogged head, or bad chips in the drive.  I tried cleaning the head with some alcohol and a cotton tip and then tried again.  Well that didn’t work, so I took a punt and swapped out the one of the  6522 VIA chips (UC2) which deals with the motor control logic.   Success the drive would now format a disk and read OK.


Tuesday, 28 February 2017

Retro LED Displays

I recently brought some of these rather nice Texas Instruments TIL311 hexadecimal displays from eBay, they are really small but beautiful.  This got me thinking, could I connect one of these displays to a micro:bit.  

TIL311 Displays

Looking at the TIL311 datasheet, I came across the first hurdle.  The TIL311 is a TTL device and needs 5v to work but the micro:bit runs at 3.3v so I needed a level shifter / buffer IC to interface between them, you could probably get away without a level shifter but I aired on the safe side. I chose the 74HCT244N but I used a 74HC244N as this is what I had in stock.

The TIL311 has a 4-bit data input A,B,C,D  which I connected to pins 0,1,2 & 8 on the micro:bit via a 74HCT244N and used separate 5v supply for the display.  To figure out how to display 0 to 9 I looked at the truth table for a 7490 decade counter and then replicated this in Python by turning the outputs on and off.

The finished project

My rather noddy Python code, I'm sure there must be a neater way of doing this.

  1. from microbit import *
  2. pins = [pin0, pin1, pin2, pin8]
  3. while True:
  4.     0#
  5.     pin0.write_digital(0)
  6.     pin1.write_digital(0)
  7.     pin2.write_digital(0)
  8.     pin8.write_digital(0)
  9.     1#
  10.     pin0.write_digital(1)
  11.     pin1.write_digital(0)
  12.     pin2.write_digital(0)
  13.     pin8.write_digital(0)
  14.     sleep(500)
  15.     2#
  16.     pin0.write_digital(0)
  17.     pin1.write_digital(1)
  18.     pin2.write_digital(0)
  19.     pin8.write_digital(0)
  20.     sleep(500)
  21.     3#
  22.     pin0.write_digital(1)
  23.     pin1.write_digital(1)
  24.     pin2.write_digital(0)
  25.     pin8.write_digital(0)
  26.     sleep(500)
  27.     4#
  28.     pin0.write_digital(0)
  29.     pin1.write_digital(0)
  30.     pin2.write_digital(1)
  31.     pin8.write_digital(0)
  32.     sleep(500)
  33.     5#
  34.     pin0.write_digital(1)
  35.     pin1.write_digital(0)
  36.     pin2.write_digital(1)
  37.     pin8.write_digital(0)
  38.     sleep(500)
  39.     6#
  40.     pin0.write_digital(0)
  41.     pin1.write_digital(1)
  42.     pin2.write_digital(1)
  43.     pin8.write_digital(0)
  44.     sleep(500)
  45.     7#
  46.     pin0.write_digital(1)
  47.     pin1.write_digital(1)
  48.     pin2.write_digital(1)
  49.     pin8.write_digital(0)
  50.     sleep(500)
  51.     8#
  52.     pin0.write_digital(0)
  53.     pin1.write_digital(0)
  54.     pin2.write_digital(0)
  55.     pin8.write_digital(1)
  56.     sleep(500)
  57.     9#
  58.     pin0.write_digital(1)
  59.     pin1.write_digital(0)
  60.     pin2.write_digital(0)
  61.     pin8.write_digital(1)
  62.     sleep(500)

Sunday, 26 February 2017

Telequipment D65

Some time ago I acquired an old 1976 vintage Telequipment D65 - 15MHz, all solid state dual-trace scope.  Unfortunately it had a couple of faults which is why it was being thrown away.

Telequipment D65

The scope basically worked but.
  1. It wouldn't turn on as the scale illumination / power switch knob was cracked and therefore kept slipping
  2. The trigger was intermittent, when powered on the triggered sweep may decide to a) start halfway across the screen, b) in the correct position and then fade or c) work as advertised.
Well the first thing I did was fix the broken knob, nothing a bit of superglue didn’t solve. This was only a temporary fix until I obtained a replacement second hand knob.  Now I could move onto fixing the annoying intermittent trigger fault. 

After a bit of digging around on the net I stumbled across this post on the UK Vintage Radio Repair and Restoration forum. Somebody else was having the same issue which could be fixed by tapping the trigger knob or the side of the case for that matter. 

Trigger, Timebase X amp & blanking PCB
Troublesome PCB

The fault was on the trigger, time base x-amp and blanking PCB.  It would seem that these scopes use doubled sided PCB's with naff though hole links which go bad with age. I re-flowed the solder on all the little links and this fixed the problem. 

Overall I'm pleased with this little scope which weighs 11.5Kg, it has made a  great addition to the workshop.  I should recap the power supply board at some stage.

Some more pictures of this scope can be found on my Flickr page.

Wednesday, 22 February 2017

A blast from the 8-bit past

I recently re-discovered my vintage VIC20 computer which was first released in 1981.  It had been hiding in the loft of plenty for some years so I got it down and decided to give it a whirl to see if it still worked.

One slight problem, the original power supply had mysteriously disappeared. I had a quick search on the online tat bazaar eBay for a replacement but alas there were none. Eventually one did turn up and after a few clicks, it landed on my doormat.

And there was much rejoicing!!!!

I duly powered my VIC20 on to see if it still worked, no magic smoke escaped YAY. I was presented with the classic start screen.

While looking for VIC20 stuff I stumbled across thefuturewas8bit website and saw the Penultimate cartridge which looked interesting. The Penultimate cartridge is loaded with 40 ROM images and has a 3-35k selectable memory expansion.   

PenUltimate  Cartridge

Magic time travelling tape.

I duly ordered one and it arrived just in time for a super 8-bit Christmas.  It was carefully packed and had some magical time travelling original Commodore logo packing tape on the box.  What a nice touch. When it arrived I gave it whirl on my VIC20, simply brilliant. Love all the old games, the menu system works a treat and it's very well designed. If you want your own then click here.

Unfortunately the good times didn’t last as my VIC20 soon failed.  When powering on it was displaying random characters, wouldn’t sync or just showed a black screen. Well that’s not good and after a bit of googling I suspected that the 6561 VIC (Video Interface Chip) chip had failed.  These chips are prone to failure due to age and they run hot.  

One bad VIC Chip

Well back to eBay to look for a replacement VIC chip, oh so they appear to be as rare as hen’s teeth. Plan B look for a VIC20 mainboard, luckily I managed to find a working tested one. It arrived a few days later so I removed the VIC chip and pressed it into service. Success my VIC20 was restored to full working order.

Replacement VIC20 Mainboard

Normal service has been resumed

Having treated my VIC to the Penultimate cartridge I recently bought myself a genuine recycled VIC20 plastic cased SD2IEC.  The SD2IEC emulates the classic Commodore 1541 Floppy Disk Drive and uses an SD card for storage.

I have to say it’s rather nice, I love the case as it matches my VIC20.  It’s another fantastic product from thefuturewas8bit.  After I imaged a SD card, I gave it a whirl well I’m really impressed.  Solid state flash memory is the future, all I can say is go buy one.

Limited edition genuine recycled VIC20 plastic cased SD2IEC

Giving my new SD2IEC a quick whirl