Generating Drum Clicks from Yamaha PSR775
I am investigating the possibilty of using the PSR775 keyboard (or any other arranger keyboard) in a band situation. The default option for the PSRS775 is to generate a full drum track, bass and accompany tracks in response to playing left hand chords.
The mixer function allows you to mute any track(s), so I could play without the drum track and the bass track. If I have a trio with a bass and drums then it is possible to make a more live sound and take advantage of the additional instrument tracks to fill out the sound.
The drawback to this is the the PSR775 does not generate a drum click track (like a metronome) which is needed for the drummer to count in the song and generally keep in sync with the keyboard.
The PSR775 does have a MIDI output however. The MIDI specification caters for synchronisation of instruments by having a dedicated timing message. This is a single byte F8 (hex) and it is sent 24 times for each beat of the bar. The PSR775 can be configured to send this timing message out of the MIDI output port. This message is sent out when the auto accompany is running and is synchronised to the current tempo.
If the reception of this message is counted, then it is possible to generate a “click” for every beat.
I designed a very simple device that plugs into the MIDI output port and generates an audio click for every beat. It is based around a PIC microcontroller and does not require any external power. The device has a 5 way DIN plug to plug into the keyboard MIDI port and has a 1/4″ jack socket for audio out and this can be directly connected to a monitor mixer input.
The click is actually generated using a one bit digital to analog convertor. A digital output line from the PIC is connected to a simple RC network (Resistor and Capacitor). The capacitor takes time to charge and discharge in response to the applied voltage. If the output is held high the capacitor eventually charges and the audio output goes to max, if the output is held low the capcitor eventually discharges and the audio output goes to min. It is possible to produce an audio waveform by switching high and low for different time periods. The audio is encoded as a bit stream of ones and zeros. The maximum switching rate is 4000 bits per second which in theory allows for tones up to 2KHz. It’s not hifi, but it can reproduce speech and simple waveforms such as metronome clicks.
I am able to program several different waveforms so that the first beat of the bar can be a bell sound.
The above is the circuit diagram using a PIC16F628 chip. An extra two resistors and capacitors are required. I constructed the device on some veroboard and fitted it into a discarded plastic pill container.
The above photos show the completed device.
The internal clock needs to be transmitted (TRANSMIT CLOCK:ON). The above shows the MIDI configuration page on the PSR775.
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I used this device successfully on a gig. I played in a trio (bass, drums and keyboards) and accompanied a singer doing mainly swing jazz stuff. I patched the audio output into a small audio mixer and plugged in the drummer’s headphones into the mixer headphone socket. The drummer was used to playing with click tracks so had no problems adapting.
To start a song, I pressed the start button on the keyboard and the drummer counted in the band. During some numbers where there was a key change, a break or a time signature change, I stopped the click track by pressing the auto start button. This primed the keyboard ready to start again. When the song resumed, I played a left hand chord to restart the auto chording and the regular click track.