December 30, 2020

Amazon "Polly"

The voices (and tech) used in Amazon Alexa, are available for anyone to play with, free of charge - search for Amazon Polly. Update: Here’s the voice of “Brian” (British English) reading Lewis Carroll with the “Neural” engine setting eanbled. Jabberwocky Poem. Try Polly yourself here.

March 15, 2020

BBC Micro repairs

I seem to have collected a few old BBC Micros - approx 1983 vintage, so coming up to 40 years old. Before powering them up, I took the advice of Retroclinic and replaced the power supply X2 capacitors that are known to fail (damaging the power supply in the process). Retroclinic can also be found on eBay. Rather than use an old-style CRT, a Samsung LCD TV provides a much steadier picture, using an RGB to SCART lead such as this.

April 1, 2018

Epic Number Battles of History: Swift 3 vs Python

Swift 3 has a “decimal” number type that can represent values such as 0.3 that are inexactly represented in Double or Float types. According to this article: An instance can represent any number that can be expressed as mantissa x 10^exponent where mantissa is a decimal integer up to 38 digits long, and exponent is an integer from –128 through 127. Note this is not the same as Python’s arbitrary-precision integer arithmetic.

October 10, 2017

Windows 10 Settings - which one?

If you go to the search bar in Windows 10, and type “settings” - there are now at least three different places you might end up: The one on the left is “System Information”. It’s been around a while. You’ll notice it reports “version” as 10.0.15063. Top right, you get to from the classic Windows control panel / System. It shows we are version 10, but gives no other information.

October 12, 2016

Shure wireless in-ear monitoring system

A friend lent me their Shure PSM300 P3T in-ear monitoring system today. This is a top-of-the-line piece of kit for weekend-warrior type bands, costing over £600 for just one monitor mix. http://www.shure.com/americas/products/personal-monitor-systems/psm-300-stereo-personal-monitor-system/p3t-half-rack-single-channel-wireless-transmitter Turns out that the actual RF signal being transmitted is straightforward analog FM. A £10 USB TV stick and the free SDR# software http://www.rtl-sdr.com/rtl-sdr-quick-start-guide/ can decode the signal and play it out of the sound card output in stereo.

November 23, 2015

Differential line receiver for Behringer Ultranet

Prototype receiver circuit based on AM26LV32 chip: The MagJack - a Bel Stewart SI-52008-F has datasheet here: http://www.farnell.com/datasheets/1731561.pdf The IC cleans up the edges of the incoming signals. With some level-shifting and AC coupling, the signals are OK to pass into an SPDIF receiver.

September 7, 2015

XMOS StartKit - write performance of Sandisk memory card

Here’s a graph showing the write performance to a Sandisk Class 10 memory card. The reason for the sharp dips in performance, are that the FAT filing system has to go off and allocate a new cluster every N writes. For example 512 byte sectors, 32Kbyte clusters, means a new cluster is needed every 64 writes. Another factor on the XMOS board is whether the code is running in ‘debug’ or ‘release’ mode.

August 31, 2015

XMOS StartKit - reading and writing to SD card

Being able to read/write information from an SD card is probably the easiest way to get large amounts of non-volatile storage into an embedded project. I’m using XMOS StartKit, with the code from here The card reader is a part from Wurth Elektronik, Farnell / CPC part number CN18143 available here. The data and clock lines have 120 ohm series resistors, as this can help to absorb transmission-line reflections on the connecting wires (even though they are fairly short).

August 24, 2015

Rigol DS1054Z digital storage scope - decoding I2S signals

I recently got one of these great little digital scopes. It has a few serial bus decoding packages (on a try-before-buy basis). You get 36 hours to play with them. Unfortunately they don’t include I2S bus decoding. I2S is a bus standard commonly used for transferring digital audio around, for example between ADCs and DACs. No matter! You can capture and export full-resolution traces of signals via a USB memory stick.

July 9, 2015

Low-noise +/-12v linear power supply for Phono Preamp

Ages ago, I built a John Linsley-Hood design of phono preamp, first published in ETI magazine in 1992. This was considerably better than the phono stage in the integrated amp I was using at the time (a Creek CAS4040). For a couple of decades I ran this from my bench power supply, so it was definitely time for its own PSU. Rather than etching my own circuit board, nowadays kits are available via eBay that save a lot of that messy work.

July 3, 2015

Simple electronic water leak detector

The following circuit is a very simple water leak detector, which I made 25+ years ago (!!) following my fiancée having a washing machine go wrong and leak all over her apartment. The circuit is not ideal - there are better designs out there. It was built with ‘what I had in my scrapbox at the time’. It’s purely analog, relying on the gain of the Darlington pair to provide reasonable on/off behaviour.

October 10, 2013

Simple Optical Compressor for bass guitar - construction

An extremely simple yet capable compressor circuit is published by Elliott Sound Products, here: http://sound.westhost.com/project45.htm Compressor Mk I I built the circuit exactly as-is (in an Altoids tin). Care was taken to optically couple the bulb to the photocell (LDR), using a perspex rod, wrapped in smooth tin-foil. The perspex came from eBay: http://stores.ebay.co.uk/thewholesaleposco2009 as did the miniature “Grain of Wheat” bulbs: http://stores.ebay.co.uk/GnA-MODELPARTS?_trksid=p2047675.l2563 This was put together, and sealed in heatshrink tubing, to make it fairly lightproof from external light sources.