Spectrum Next – Blinkenlights Part 2

Research – Too many rabbit holes and a surprisingly large number of ways this can be implemented….

The First Prototype



For those inserts to transmit light – They have to be translucent 

I got a batch knocked up with a reasonably localSLA Printing company – 3D Folkes– doing stuff this small and detailed can’t be done easily with standard FDM printing. I don’t own an SLA printer and can’t justify another gadget – even if there’s a good usecase. The cost of entry for a reasonable SLA printer and enough resin would be at least £500, and add the learning curve……..for a few small batches, having an expert do it is worth it.


The Circuit used….

The Spectrum Next has a conveniently located header of pins – J15 – See the Wiki Page here –   Just below the Coloured inserts in the case….


It makes sense that any powering LED’s would be done from this header, it’s very close, has the needed voltages.

It also has an i2c connection…………..

That’s Great – it now means that there’s a possibility of controlling the on/off of the LED’s from the next! – someone [better at software than me] could bake commands into the firmware to , say flicker the Yellow LED on wifi activity, or pulse the blue LED if an enemy is too close in a game…Or, Or….


I2c LED Control

There’s a LOAD of ways to control LED’s via i2c. After another few rounds of googling,

One i’ve decided to try is the PCF8574

This is an 8 Bit port expander – simply send an i2c command to it. it selects an LED


Some LED’s and an ebay special PCF8574 board….Cheaper than buying the chip!


How much power can these chips handle!? – can they do 8 LED’s running at 20mA each?

According to TI- one of the makers of the chip


Kind of……For the whole chip………..

ABSOLOUTE max Chip VCC-GND current = 100mA

8 outputs = 12.5mA per output

or 4 outputs at 25mA each……….MAXIMUM

TI suggests to keep it significantly less for continuous – below 50mA = 6.25mA per output

or, 4 outputs of 12.5mA……….That should be enough to get the LED’s nice and bright 🙂


The Circuit – and code – Found here –




And, The Result


D’oh! – Far from perfect coupling of the LED’s to the lightpipe long parts of the inserts….BUT that diffusion is terrible.

Back to the drawing board a bit? –

I’ve about 2.8mm width x 2.8mm height to play with. I recon I can fit some LED’s INSIDE the channel for the inserts.

More research…………..


Author: Bleugh

Early Fourties, Wife, two kids in primary school. Both of us work full time...5 years now we’ve been Back in Blighty after a decade away...It's a new country for everyone! Still finding time to tinker!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: