Guitar pedals are harder than they look – at least this one has been. I’ve learnt some valuable lessons that I’ve never had to worry too much about before. The most valuable lesson is that noise is not fun. Living in the digital domain is brilliant because is it far less affected by noise. Analogue is the complete opposite.
If you remember from last time, I had to bias my guitar input at Vcc/2, so that I could feed it into my first op-amp. This meant that any noise present on the voltage rail was put straight on my input, and amplified – not a good start. Thankfully, all is not lost as I just need to convert the input stage to an inverting op-amp with the reference set on the non-inverting input. It should just be a case of moving a few components around as I has enough forsite to scatter passives around the op-amp.
In the meantime I want to talk about my TV. It is a low-end 32inch LCD Hitachi with IO that fits the price tag – no USB, only 2 HDMI, Component, Composite, and VGA. It’s pretty basic, but it fulfils MOST requirements of it, and was a bargain when we bought it. However, over the last two years my needs have changed, but I cant justify buying a new TV. I’m sure modern TV’s are extremely complicated, but like all good hackers/engineers, I needed to know just how complicated. More than a few years ago I would have just taken the back off and gone oscilloscope crazy, but I’ve learnt my lesson by poking around inside said oscilloscope so instead started with the service manual.
In fact I started by searching for spares for my TV (Hitachi 32LD30UA). That gave me a part number of my main control board – the Vestel 17MB35. I can only assume it is a popular control board, purely based on the amount of information I can find about it. Amazingly I found a service manual on the ArgosSpares website. I don’t know why I say that’s amazing, as Argos is where I bought the TV, but I didn’t expect to find a service manual there. Anyway, hunting through the manual I found out that my control board should have footprints for 4 (not just 2) HDMI connectors, 2 USB connectors, and even a “Ye Olde” DSub9 connector. Thinks were looking up, as I needed a USB port just to power my Raspberry Pi. I have been tempted to open the back of the TV and piggy-back off of a voltage regular, but not all I need to do it fit a USB socket instead – a nice and clean modification.
At this point, I still haven’t actually opened up the TV, but I have ordered and received a spare control board. I figured when I eventually open the TV I can copy the contents of my TV’s EEPROM into this board, and see what happens when I switch them over.
My aim is to have the Raspberry Pi powered from a USB port on my TV, have a third HDMI channel, and enable HDMI-CEC. I am pretty confident in the USB power, but who knows about the rest – wish me luck.