ADVANCED SCRATCH CODE PDF SERIAL

It implies on a Single-Face board with as few jumpers as possible. Of course, the switching scheme had to be tested before going on, but luckily, it worked very well!! DIYable BoardĪ second challenge was to make this shield DIYable. The channels choose to be multiplexed were from the 'light' and 'sound' sensors, since they have stabilizing (filter) capacitors, which make changes in such channels to occur much slower than the switching. To accomplish that, the solution found was to implement a multiplex using a 4066 that is a quad bidirectional CMOS analog switch. One at a time each switch is activated and the correspondent ADC channel is read. If you know Arduino well and paid attention to the last step, you might be noticed that Scratch expects to receive 7 analog readings, but a Stardard Arduino has only 6 channels. This is good, because if suits well with Arduino ADCs resolution.įor the Scratch Board Release 1 firmware and Scratch release 1.1 and later, the mapping between channel ID and sensor type is given below: Channel / Sensor 0 / Resistance D 1 / Resistance C 2 / Resistance B 3 / button 4 / Resistance A 5 / Light 6 / Sound 7 / Slider 8-14 / Not Used 15 / Firmware ID (0x04)įrom the 16 possible channels we have 7 analog, 1 discrete (on/off), 1 dummy (firmware-id) and 7 spare (not used now maybe in a future version). The high byte / low byte pairs contains a 4 bit channel ID and a 10 bit Value. 18 bytes) spaced in time by a 400us interval. The request packet is simply a byte with the value 0x01, whilst the sensor data consists of 9 high byte / low byte pairs (i.e. First Scratch application send a a data byte to the board then the board replies with sensor data. The protocol between Scratch and Sensor Board constitutes of a ping pong mechanism.

ADVANCED SCRATCH CODE PDF SERIAL

It is good, because Arduino already have a Serial Port which means less circuits to implement. The first thing to do is read the documentation ( here) to find how do the Sensor Board interacts with Scratch.Īfter some time reading we found that the Sensor Board communication occurs via RS-232 at a speed of 38400 baud.

Advanced scratch code pdf