Measures for synchronizing the GSV-6BT via digital IO lines
the master can send the synchronization signal either through SW1 or SW2 digital output. So, for the SYNC line, if SYNC master is configured for SW!, it must be:
Connect GSV-6BT_1 Pin 38 to GSV-6BT_2 Pin 39
Connect GSV-6BT_1 Pin 38 to GSV-6BT_3 Pin 39
If SW2 is used for Master sync output:
Connect GSV-6BT_1 Pin 37 to GSV-6BT_2 Pin 39
Connect GSV-6BT_1 Pin 37 to GSV-6BT_3 Pin 39
Of course, the GNDs of all three devices must also be connected together, e.g. using pins 26.
The digital IO configuration must be done only once, then the devices store this parametrization. This must be:
Launch GSVmulti, connect to GSV_6BT_1, configure Digital Output 1 (SW1) or 2 (SW2) as Master
connect to GSV_6BT_2, configure Digital Input 4 as Slave
connect to GSV_6BT_2, configure Digital Input 4 as Slave
The other question is, how to start the quasi-synchronized recording on SD-card .
This is a "longer story", not yet fully documented.
To make it short:
1. Starting the recording simultaneously is generally not possible (because the functionality of the file system FAT32 doesn't allow this and the RTCs aren't synchronous).
2. To give the user a possibility to re-sychronize the different files of the several SYNCed GSV-6BT, from firmware version 3.30 (improved in 3.37) I did a little trick: About 200 ms after the recording was started in the master device, the master writes the letter M at the end of one particular measuring values row and at the same time, the slaves write the Sync marker S at the end of the row.
3. The starting recording behaviour is different, depending on how the recording was started:
- By software (GSVmulti): The sync marker is written by the slaves only if they are already recording, so here it's recommendable to start the recording with the slaves first, then the master.
- The recording can also be started by hardware, using a switch. This switch must then be connected between the TRIG input (pin 39) and GND of the master. The Digital Input No. 4 must be configured as "Trigger File Log". Then. if everything is configured correctly, with this switch, the recordings of all 3 devices can be started together, if the software is NOT connected, i.e. if the blue BT LEDs of all devices are off, but the green POW LEDs are on. To achieve the latter, the GSVon/off state must be configured to "GSV remains on" in the Bluetooth settings menu (Advanced device settings -> Interface -> Bluetooth).