Spectrum Next – Blinkenlights Part 2

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

The First Prototype

img_0767

 

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….

1200px-NEXT_GPIO

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

img_0761

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

https://e2e.ti.com/support/interface/f/138/t/423120

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 –

http://www.valachnet.cz/lvanek/diy/homebrain/index.html

 

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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!

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