At the Motorcycle Safeguard with Touch Censor, we’ve created a mechanism to make relay on if the sensor is touched and remained active even though the hand had been released from the sensor. With only one sensor the security of motorcycle is pretty good. However, sometimes people like to overdo in acting. Therefore, some people think that security would be more powerful if there are two sensor, and both sensors must be touched concurrently so that the relay can be active.
To increase the number of sensors is actually not a difficult thing. You simply add the PNP transistor to serialized with Q2 in providing base current for Q1.
Note that we only make the circuit of Q2 becomes twice with exactly the same form, then arranged in series.
In the same way, you can also increase the number of sensors into three, or even four. Please try to ❗