Sorry, I now read that you wanted a solution without external hardware. Then my solution with the Keystep wouldn't work for you.
In that case I don't think there's an easy solution. In my tracks where I'm using an LFO as clock I just slowly fade things in via the mixer rather than abrupt start and stop. I would then hook up everything to that one LFO to keep things in sync.
You are not missing anything obvious, sync-ing start and stop without midi or a dedicated clock module is difficult.
But you can use the VC switch like this : put the pulse out of the LFO in one of the inputs, and leave the other input empty. Then use the output of the switch as your clock. The problem with that is that it won't start immediately, only at the next pulse. But you could do that. There is no module for a manual gate, so we're going to use a +5V signal routed to an attenuator (for example the 2ATT/CV). Patch the output of the attenuator (turned all the way down for now) to both the LFO sync in and the switch gate. Like that, when you turn the attenuator all the way up, it will act as if you just opened a gate, and will at the same time reset your LFO and open the switch to let the clock signal through.
I haven't tried it but it should work, let me know how it goes.
Thanks for the tips guys. Gaetan I don't have the VC switch module but I tried feeding a 5 volt signal to the sync input of the lfo and it doesn't seem to work as a reset. It just produces an extra pulse in between and then continues with the pulses in the same Tempo.
I also tried triggering via midi a vco and routing it to the sync. The lfo does sync but not exactly when you press a key.
So it seems the lfo is always free running. It can sync but not reset
Using an LFO is really just for simple clocking scenarios.
In your case you probably want to use an external MIDI clock which not only has clock pulses but also start triggers which you can use to reset sequencers and start them in sync.
Otherwise you might have to live with the free running LFO and maybe a small delay between pressing your button and the sequencers starting. You can still reset the sequencers though and make them start in sync on the next LFO pulse, using your button.
I guess you need to feed +5v simultaneously to the LFO (SYNC) and the (TRIQ164 RESET). I tried it using a MULT with +5v from the MASTER. Just touching the MULT with the tip of the cable makes a really basic button. If you want a physical button you can use the button in the 2ENV module (either one) patching the corresponding 2ENV (OUT) to the MULT. In both cases it starts inmediately.
If you need to stop the sequencer, you'll also need a gate to stop the LFO feeding the sequencer, so I'd connect a switch (physical switch) inbetween, ideally a DPDT with one side handling the trigger for the sync/reset of the LFO and sequencer, and the other one as a gate for the LFO signal.
Sorry, I just understood that the LFO doesn't sync when you feed it +5v.