1. Fitted basic optical encode circuit to my , now figuring out optimal settings for calculating wheel speed. Notes:

```Sane gurdy speed of 14 revs every 10 seconds = 1.4 RPS
52 markers on wheel = 52 * 1.4 = 72.8 transitions per second ≈ 73Hz minimal input signal

Timer nominal input freq is Fosc / 4 = 4MHz / 4 = 1Mhz
Max prescaling = 1:256, i.e. TMR0 increments once for every 256 Fosc/4 pulses
Resultant timer freq = 1Mhz / 256 = 0.00390625 Mhz = 3906.25 Hz

Input signal has ≈50% duty cycle so periods between pulses should be 1 / 73 = 13.69863014ms

Period of 3906.25Hz wave = 0.256ms
Num pulses @ 3906.25Hz after 13.7ms = 13.7 / 0.256 = 53.515625

1.4 RPS is minimal normal gurdy trompette playing speed, so counting 54 clicks per transition gives a little space for speeding up and a lot of space for slowing down.

High gurdy trompetting speed of 24 revs per 10 seconds = 2.4 RPS
TPS = 52 * 2.4 ≈ 124.8 = 125Hz maximum input signal = wavelength of 1 / 125 = 8ms
Num pulses @ 3906.25Hz after 8ms = 8 / 0.256 = 31.25
```

So these values should give a just-wide-enough span of ≈20 ticks between nominal and trompetting speed, with room to halve or potentially even quarter the prescaler if this turns out to not be enough. One advantage of these values is space to track much slower wheel movements, opening this up to be used for slower performance tools as well as speed measuring.

An external switch could always adjust the prescaler if necessary to cover both use cases.

2. Had to repair my headphones yet again so went to @hakkavelin, started experimenting with wheel speed measuring devices. Got a basic Vishay CNY70 reflective optical sensor circuit working, soldered into my PIC demo board for initial testing before I make a tiny package to go on the gurdy itself.

(all PDFs unfortunately):

3. Returned to Iceland to find RTC chip free samples waiting for me @ Vísar HQ, solidifying maximintegrated.com as my favourite semiconductor company — samples shipped to Iceland, of all places, arriving within days of being ordered.

4. # Voltage Dividers

Working through some example circuit simulations I finally gained an intuitive understanding of the voltage divider equation — it’s just a ratio, but I had never figured this out before.

Given this circuit, where the voltage source is rated at 1V:

The voltage at A is equal to `1V·(R2 / R1 + R2)`, which is `1·(1/1+1) = 1·(1/2) = 0.5`.

Why? Because `R1 + R2` represents the total resistance of the path, and as such the total voltage drop. Dividing R2 by the total produces a fraction representing the voltage drop over R2. Multiplying the input voltage by this fraction leaves us with the voltage dropped over just the R2 portion of the circuit, which must be VA because there are no other branches in the circuit.

Put another way, the equation finds the ratio of resistance (and so voltage drop) `R2:R1` and then feeds the input voltage through this. Here’s a more abstract visual representation of what’s going on:

5. # Anyone recommend a nice little, simple, easily available single/dual channel audio amplifier IC? One that's nice and simple, only requires a simple supply and a few external components? #electronics #audio

Anyone recommend a nice little, simple, easily available single/dual channel audio amplifier IC? One that's nice and simple, only requires a simple supply and a few external components?

6. # Yep, that's what I usually feel when reading component #datasheets. Especially when looking at graphs other than nice simple IV curves. #electronics #funny

Yep, that's what I usually feel when reading component . Especially when looking at graphs other than nice simple IV curves.

7. # Just re-posted some of my old tutorials and guides for using old #legomindstorms — How to program the #RCX on Mac OS X, how to make it speak VLL, and a calculator for #homebrew sensors. http://waterpigs.co.uk/electronics/mindstorms/ #robotics #electronics

Just re-posted some of my old tutorials and guides for using old — How to program the on Mac OS X, how to make it speak VLL, and a calculator for sensors. http://waterpigs.co.uk/electronics/mindstorms/