Category Archives: measured

measured, snippet

What does “Barometric pressure inches” mean at Weather Undeground API and

Weather Undeground wants the pressure in their API (http://wiki.wunderground.com/index.php/PWS_-_Upload_Protocol) as “barometric pressure inches” which is the same as “inches of mercur” or inHg or just hg. Notice that it changes based on temperature.

Millibars aka hPa (the one’s around 1000) can be converted to Hg by multiplying with 0.02953 when tempeature is 32 fahrenheit (= 0 celcius, the water freezing point).

So: barometric pressure inches/inches of mercury/inHg = millibars/hPa * 0.02953

More here: http://www.csgnetwork.com/meteorologyconvtbl.html

measured

BOSS RC-50 Loop pedal

Some snippets from BOSS RC-50 Loop Pedal:

– At software version 1.0 the MIDI sync is quite useless and it’s not working as promised. See following discussions/links:

  • http://forum.ableton.com/viewtopic.php?p=725255&sid=4ef406981f91b3c9fc3feb2b92b4db2d
  • http://www.fretbase.com/blog/2009/02/boss-rc-50-loopstation-flawed-but-glorious/
  • http://www.em411.com/forum/8555/1/242445/Boss_RC50_looper_midi_sync_with_laptop.html
  • http://reviews.harmony-central.com/reviews/Effects/product/Boss/RC-50+Loop+Station/10/1

– MIDI CC (Control Change) command can be used to control the pedal in some ways. Setting tempo is quite bizarre, the value (0..127) is not linear to tempo.  Some measurements (first value is the third byte aka second CC value, where CC#1 consists of bytes 176+1+BPMvalue and CC#80 is 176+80+127 where 127 is constant since RC-50 doesn’t take any values in CC#80 messages) :

  • 127 = 250.1 BPM
  • 115 = 230.1 BPM
  • 80 = 172.2 BPM
  • 40 = 106.1 BPM
  • 10 = 56.5 BPM

– Touching the wheel selector changes your patch and you will loose all phrases without warning. This is quite nasty. This happends even you set the patch range to 1..1. When you touch the selector wheel the patch doesn’t change but it resets the patch to what you haved saved before.

electronics, measured, oscilloscoped

MIDI signal

MIDI signal in oscilloscope. Inverted serial 31200 bits per second. Captured from USB->MIDI adapter (SWIS). First bit time is about 32us (31.2us = microsecond ). Voltage difference was 3.92V.

A great page describing MIDI: http://www.tigoe.net/pcomp/code/serial-communication/midi which describes MIDI like:

“MIDI is a serial communications protocol, operating at 31,250 bits per second. Each byte has 8 bits, plus a start bit and a stop bit. It operates at 5 volts DC. The standard MIDI connector is a 5-pin DIN connector, and usually all connectors on the device are female, and both ends of a MIDI cable are male.”

From here http://home.roadrunner.com/~jgglatt/tech/midispec.htm :

  • MIDI is an asynchronous serial interface.
  • The baud rate is 31.25 Kbaud (+/- 1%).
  • There is 1 start bit, 8 data bits, and 1 stop bit (ie, 10 bits total), for a period of 320 microseconds per serial byte.
  • The MIDI circuit is current loop, 5 mA.
  • Logic 0 is current ON.
  • To avoid grounding loops and subsequent data errors, the input is opto-isolated. It requires less than 5 mA to turn on. The Sharp PC-900 and HP 6N138 optoisolators are satisfactory devices. Rise and fall time for the optoisolator should be less than 2 microseconds.
  • The standard connector used for MIDI is a 5 pin DIN.
  • Separate jacks (and cable runs) are used for input and output, clearly marked on a given device (ie, the MIDI IN and OUT are two separate DIN female panel mount jacks).
  • 50 feet is the recommended maximum cable length.
  • Cables are shielded twisted pair, with the shield connecting pin 2 at both ends.
  • The pair is pins 4 and 5. Pins 1 and 3 are not used, and should be left unconnected.