Thursday, 11 September 2014

Ohm on the range

Visit Tagbits to see the full range of tagger products described in this blog.

I've been asked to make a large lasertag sensor harness for a client. This comprises of six Tagbits lasertag sensors on a single lead.

I was asked for four of these, three worked perfectly but the last one had a short between the power lines (+5V from a 7805).
A visual examination did not reveal the fault, and as I didn't fancy disassembling each sensor one by one I wheeled out my Polar Instruments Toneohm 700.

This is no spring chicken being last manufactured in 1988. But it's a great piece of kit having a 200mOhm (milli Ohm) range, and audio feedback with a higher tone indicating less resistance.

My normal multimeter in continuity mode indicated a short no matter where in the cable the probes were placed. But the Toneohm didn't even register a connection between +5V and 0V on any sensor until I tested the sensor that actually had the fault. e.g. It is so sensitive it registered open circuit along a 60cm piece of wire which was shorted at one end.
In fact, it's so sensitive it could detect which side of the PCB the fault was on:
Between the +5V and 0V connections on this side of the PCB, the resistance is 93.9mOhm.

But on the other side of the PCB, the same connections show 49mOhm, indicating the fault is on this side of the board.

And lifting the PCB showed a single strand of cable between 0V and 5V. Problem solved.

Monday, 25 August 2014


Visit Tagbits to see the full range of tagger products described in this blog.

This week I've found time to make the control unit for my CNC router. It's standard Longs stepper controllers with a switch mode PSU and a parallel port break out board.

I 3D printed a mount for the connectors to the stepper motors and limit switches, and I've wired using bootlace ferrules to make it a bit neater.

The mains connection to the PSU was open, so I 3D printed a small cover for it on my Mendel90:

Friday, 8 August 2014

CNC Router..continued

Visit Tagbits to see the full range of tagger products described in this blog.

I've been really busy with LaserTag stuff..but recently I've had chance to resume my CNC router project.

This last week I plucked up enough courage to drill the £75.00 worth of aluminium I bought for the Y axis, it's 1500 x 550 x 15mm in size:

My simple Clarke pillar drill is woefully inadequate for this job.

Stage one was to spray mount a 1:1 2D print, (using my A0 printer), of the holes that I needed to drill in the ali plate:

Using an optical centre punch and the large bench at HacMan I centred all the holes. My colleague Ian at work drilled, counter bored and countersunk the holes impeccably using the Bridgeport vertical miller we have there:

Need to plumb in the motor next...

Sunday, 27 July 2014

Google Cardboard...impressions

The first time I heard about Google Cardboard was when the lens supplier I use for my LaserTag kits informed me they were out of stock due to demand.

With my interest aroused, I sent off for a kit from ebay: This turned up with some velcro fasteners, pre cut lens holes, glass lenses and instructions:

After half an hour with a scalpel and some super glue I ended up with this:

I found that the kit supplied triggered the power switch, and the volume switch when closed. I cut some holes to prevent this:

What's it like?.....amazing. Occulus Rift it is not...but for $30 it gives you an insight into the world of VR. I suggest you buy the cheapest copy of it that you can and try it. May I recommend: as a starter.

Manchester Mini Maker Faire

I visited the MOSI mini maker faire this weekend and took a few pictures. It's a really small event compared to others in the world. However, 'owt is better than nowt and it's great to see local makers turning out to support this event in its third year.Having 3 under 12s with me meant I had little chance to take all the pictures I wanted to. I got some though...

There was a soldering workshop in the main foyer. The task was to build a simple circuit which comprised of a battery, switch and a couple of colur cycling LEDs. My posse had a try..and did quite well considering it was their first time at soldering. Credits to the guys on the stand who had the patience of saints.....

An artist called "Dutch Cyclist" had mad life size Lego heads that the kids found enticing.....

The majority of the Makers were house in the 1830 Warehouse. This was the first railway warehouse in the world, and seems an appropriate place to encourage innovation:

Leeds Hackerspace had a cool water feature which incorporated a LED strobe. This slowed down the water stream to give a really cool display that my youngest found irresistible.

Leeds were also showing a large RGB LED cube that looked great:

York Hackerspace had a great space themed game that required players to co-operate with eath other to win:

Hacman, my local Hackerspace had a stand showing what the members have been up to:

Sunday, 20 July 2014


Visit Tagbits to see the full range of tagger products described in this blog.

I believe the technical term is 'a failed print'

Saturday, 31 May 2014

As real as I can (legally) get it

Here in the UK gun laws are (rightfully) tight. However blank firing replicas are legal. I was asked last year to develop a Lasertag system that detects a blank round being fired, and sends a Lasertag pulse in response.

My first challenge was to detect the firing of the blank. Initially I developed a circuit which used a piezo sensor to detect the shock from the blank. However this was very susceptible to noise and was unsuccessful.

My second attempt utilised a neodymium magnet attached to the rear of the Glock slide. This, in conjunction with a Hall effect device encapsulated in a 3D printed mount within the carbine kit. The recycle time of the Glock replica was about 70ms as timed with this jig:

Here the hall effect sensor is mounted behind the Glock blank firer. Checking the timings on my scope showed this:

Tweaking the software to only shoot when a pulse of approximately 100ms or less prevents shot packets being sent when a human cocks the gun. There is no way a human could pull the slide back and release it in 100ms.

This allows maximum realism. The only way to fire a Milestag shot is if there is a blank up the spout. When the clip is empty, it must be physically reloaded before anther shot can be fired.

Looks pretty good when fitted to the carbine kit with 3d printed focus tube and a small project box from ebay. Both are fitted to the picatinny rails of the carbine with 3d printed fixings.

However....multiple shots through the carbine kit resulted in it's destruction..and a trip to the doctors for an X-Ray. We only managed to video one shot...with a following misfire. Proved the concept though..Watch this space...

Update 3 Jun : Some people have expressed concern as to the safety of the blank firing replica. I'd like to point out that the barrel is physically blocked with a plug of titanium and falls under the none licensable category of replicas under UK law. (See below).Absolutely nothing comes out of the barrel when the replica is fired. All the chemical energy does is make a bang and cycle the slide.
They are loud, and hearing protection is preferable but nothing, no projectile or wadding or even gases leave the muzzle.

UK Law on blank firing replicas:

"What are Blank Firing Weapons?

Blank firing weapons generally fall into two different categories:

Those not requiring certification

These are imitation firearms, not readily convertible into a firearm to which section 1 of the 1968 Act, as mended, applies. These "firearms" are not firearms within the definition of section 57 (1) of that Act, and therefore are not required to be held on a certificate. (see "What are imitation firearms?")

Such weapons are capable of firing, or capable of being adapted or converted to fire, blank ammunition. With blank ammunition no shot, bullet or other missile is discharged from the barrel - you just get a "bang" and maybe a puff of smoke.

Such weapons are often used in battle re-inactments, theatre and TV productions and for starting races."