Electronics Store Maplin Closing - The End of an Era

Introduction

As a teenager in the late 80's, I was really into electronics. Back then you could build useful circuits for a reasonable cost, making things that were otherwise expensive or unavailable. It was a great hobby to get into, I wanted to be an electronics wizard (although that name seems silly these days) and I considered at some stage I would get a job within the electronics industry. I would regularly read 'Everyday Electronics' magazine, not only for the articles and build details, but for the adverts, and it was on one of these pages that I discovered an electronics mail order company who sold a chunky catalogue at W.H.Smith for just a few quid. It had amazing cover art, details about a huge range of electronics components and included suggested circuit diagrams for most of their semiconductor components. I bought one every year, it became my faithful companion for my many projects and hobbies... and so began my thirty year plus relationship with Maplin.

The Rise and Fall of the Catalogue

The first catalogue was just 28 pages back in 1972, the year the company first started. But it soon became an impressive tome with well organised sections, filled with clear diagrams, data charts and product photographs. You knew exactly what you were buying, and you received exactly what you'd seen. It's not surprising that Maplin was so successful.

Some of the Maplin catalogues from the 80's borrowed from This Blog

As the years went by, the rise of computers and microprocessors had a huge impact on the industry and Maplin did a reasonable job in keeping up with changes in the market. Add to this the flood of cheap Chinese goods entering the country and making your own stuff became a non-starter. They started to stock computer hardware, but PC technology changed too quickly. These items often became obsolete or were overpriced as soon as the catalogues came out. The company was able to mitigate this problem when they created their website, but the result of this was that most people didn't need the catalogue anymore. I still bought one from time to time, but when you knew a reasonable percentage of stock would be unavailable, it no longer seemed relevant.

The Rise and Fall of The Store

The company expanded the number of stores to over two hundred, every town seemed to have one, but I still liked the convenience of mail order. They diversified into consumer products like gadgets, phone accessories, lighting, disco equipment, home security, kids toys and hobbies. Clearly they weren't going to be able to support shops like these by selling LEDs and 555 timers, but each store still sold a limited quantity of components from a counter at the back. They hadn't totally sold-out, but they lost a lot of credibility by selling cheap crap at hiked-up prices.

The company has been acquired by a number of owners over the last thirty years and it was with sadness that I started seeing news articles this year that revealed Maplin was in trouble. Shortly afterwards PwC were called to act as administrators and attempts were made to find a new owner. The reasons cited ranged from a drop in the value of the pound caused by Brexit, to the withdrawal of credit insurance which made it impossible for them to raise capital. But I don't think we should ignore the impact of online services who could easily under-cut their prices. It may just be another one of those high-street tragedies,.. another bricks and mortar company floundering in wake of online retailers like Amazon.

Just another store closing in this Derby Retail Estate

I wouldn't like to say how much I've spent at Maplin over the years, it's always been my go-to store for bits and bobs. But more recently I've found the store seemed to be a little out of touch or less useful than it used to be. As they cut the number of SKU's to reduce cost, I've found myself turning to eBay for those more obscure items. Nevertheless let's consider for a moment how convenient this place has been. How many stores are there where you can easily go for a cable to connect your USB keyboard to your iPad, a spool of solder, or a couple of metres of speaker cable and take it home that day?

Maplin - Closing Down Sale

I've visited the Derby store a few times over the last week, there's a huge sale on with typically 30% off most products. There's some great bargains, but I wish it wasn't so. For my whole adult life you have been there for me Maplin and I will miss you greatly.

Hacking a Solar Security Light

Introduction

I've got a few LED lights around my home with infrared motion detectors. They provide soft light at night in the hall, stairs and inside cupboards, and another provides a surprisingly bright light over the back door. So no more fumbling in the dark for light switches or keys on cold dark nights. But the one thing that's been bugging me is the light in the garage.

I replaced the single light fitting with a 6 foot fluorescent tube last year. It does a good job lighting the space, but the kids sometimes leave it on, and the second or so delay is annoying if you're repeatedly going in an out of the side door.

Having been impressed by the light over the back door I decided to get another for inside the garage. Not only will this provide some convenience, but solar = free power.

Problems With the New Light

Solar LED Light

I picked up this 36 LED light from Maplin which provides 150 lumens and has a sensor range of 8 metres. Not bright enough to do any work by, but enough to stop miscellaneous clutter from being a tripping hazard.

It was different from the previous one I'd bought, being a bit cheaper, and the on-line reviews showed that some had problems with water getting in. But as I'd planned to install it inside my garage, I disregarded that as a problem, and purchased the light.

It wasn't until testing that I realised the light wouldn't come on in daylight. (this is determined by measuring the voltage coming from the solar cell). I found I had to cover the solar panel with my hand, or disconnect it to get the light to come on.

This was NOT good!

Hacking the Light

I mused that perhaps the circuit could be altered so that the solar panel only charges the battery and doesn't factor into the sensor circuit. I grabbed my screw driver and started to investigate.

After removing the screws from the main case I found a 3 cell battery pack and a small circuit board.

The light's casing open showing circuit board.

You don't get wiring diagrams these days so I had to trace the circuit and sketch it out on scrap paper.

1. The voltage from the solar cell passes through the blocker diode D1, which then feeds onto the battery connected to the (slightly blurred) white connector.

2. The white return wire from the IR sensor connects to the OUT pad on the circuit board, which feeds the base of larger transistor on the far left. This turns the light on when the sensor is triggered.

3. The smaller transistor Q2 shorts the base to 0v if the voltage through R4 (from solar cell) is high. This stops the light coming on in the day.

Remove R4 from the circuit.

So,.. I grabbed my soldiering iron and desoldered this resistor.

The removed resistor on my finger

Bingo, the light comes on, and this time I didn't have to cover the solar panel.

Raspberry Pi Diary - Scratch GPIO and 7 Segment Displays

Installing Scratch GPIO

The standard version of scratch can't control the GPIO, so you need to install ScratchGPIO7 before you can play with LED's and switches. I googled the install instructions but here they are if you need them:-

wget http://bit.ly/1wxrqdp -O isgh7.sh

sudo bash isgh7.sh

If you need to add the desktop icons to other users you can specify user name on that last command:-

sudo bash isgh7.sh fred

(nb. make sure you have an internet connection first!)

Use the new desktop icons to start scratch and it will ensure a background python task is running that enables the GPIO control.

There's a simple code example that toggles pin 11 between low and high. We attached an LED to this pin, (using a 470R resistor) and connected the other end to one of the ground pins. (doesn't matter which)

Success - a flashing LED!

Moving on from Basics

The plan was that I'd set my 8 year old a task of driving one of his 7 segment displays using the Raspberry Pi, and maybe get it counting 0 to 9.

It seemed like a suitable jump of of complexity both in software and breadboard wiring. (perhaps it was a jump too far) Here's what happened!

Circuit Debugging

My son disappeared for half an hour and returned with breadboard, 7 segment display, and T-Cobbler carefully connected with jumper wires. He plugged it in to the RPi, loaded up the pin 11 demo program and clicked the green flag icon to run the program. The scratch variable was clearly cycling on and off on the screen, but none of the segments lit. We ended up tearing the circuit down trying to get it to work and along the way discovered a few problems..

1. The T-Cobbler board has 40 pins that need to be inserted into the breadboard. That takes more insertion force than you'd think.

2. The LED display was of the common anode variety. This means that all the anodes are connected together and the segments lit by pulling the individual cathodes down to ground.

(So he had connected the LED segments the wrong way round.)

A quick flick through the Maplin catalog confirmed you can get common cathode versions.

Driving Common Anode Displays

My initial thought was we'd have to use a transistor inverter to drive each segment, but that's a fair bit of extra complexity and not strictly necessary.

A simple inverter circuit is not necessary.

Each GPIO output actively pulls high or low, so if you connect the common anode to 3.3v then any low pins connected to the cathodes will turn the display segment on.

Connecting a common anode display to a Raspberry Pi

The only hitch is the logic is the other way around! (pin low = segment on)

But it's only just occurred to me that we could do this after reading the Raspberry Pi GPIO Documentation and seeing an LED connected this way. (Must try this tonight!!)