HP2VGA: Project Write Up

Introduction

This project started about two and half years ago when I took an FPGA class at MIT and the professor happened to give me an HP1662AS logic analyser that MIT were throwing out. Despite the fact that I lived in the UK and this thing is massive and weighs 20kg I took it anyway. I thought it would be a cool project to replace the cathode ray tube with a larger, LCD display. I thought I would get this done before I left the US three months later… Little did I know it was going to take me another two years (although not of continuous work). Now I am nearly done, and just in time to ship it back to the US when I move back for work.

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The HP1662AS on the desk where it was left for me in MIT

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Project: Spectrum – Filter Design

Frequency Response

As I said in the previous post, I want my filters to perform in the same way as the MSGEQ7. The frequency response of this chip is given in it’s datasheet.

MSGEQ7_Frequency_response.png

The 7 frequency band responses of the MSGEQ7

From the datasheet I can see that, to replicate this response, I will need 7 bandpass filters at 63Hz, 160Hz, 400Hz, 1kHz, 2.5kHz, 6.25kHz and 16kHz. Each filter will need a quality factor of 6 (this basically sets the bandwidth of the filter).

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Project: Remoteli – Finished

It’s been a long project. I think this is due to a combination of factors – a large number of manufactured parts, fiddly soldering and software troubles. Certainly at times I have struggled to find time to work on it, worsened by spending the year studying in America rather than the UK. Getting back into the project after waiting two weeks for a board to arrive was a challenge I faced more than once.

Nonetheless, Remoteli is now complete! (At just 39x18x4mm ignoring nuts and bolts)

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Project: Remoteli – Plastic Spacer

Remoteli’s construction will be a PCB (the one I already have with all of the buttons on it), a plastic layer which is 1.6mm thick, and another PCB on top to cover all of the electronics, except for the switch, IR receiver and transmitter, and the buttons.

Today I finally managed to hunt down a 3D printer in order to print out the plastic spacer. Here are my designs:

It turned out a friend of a friend had a 3D printer I could use.

Being a small model, it only took 12 minutes to print and it came out pretty well. Unfortunately the detail around the screw holes and the top of the circle didn’t print well, but it was good enough to work. I didn’t really expect it all of come out perfectly anyway.

Here it is:

spacer and board

I was impressed how well the battery fit into the spacer. Now I am just waiting for the second board to arrive from OSH Park.

Project: Remoteli – Design

This remote needs to be small, and the components need to be even smaller. This means I’ll be using only 0603 passive components. The microcontroller I will be using is an Attiny1634.

I thought about a few uCs before I chose this one, but I settled on this for a number of reasons:

  • It comes in a tiny 4x4mm QFN package
  • It has 18 I/O lines which is enough for ~12 buttons, an infra-red LED and an infra-red receiver
  • It has 16K flash which means I have a lot of memory in which to store learned infra-red codes

In order to learn new codes the remote needs an infra-red receiver so it can copy codes from existing (larger) tv remotes. This was a harder design choice, but in the end I settled on this a TSOP572. This is one of the few infra-red receivers I could find that had a low enough profile (<1.6mm) to fit between the two circuitboards.