Some video cameras have a socket w for a remote control unit. It appears, however, that it is not always easy to connect and interval-control to this socket. For instance. the Blaupunkt 8010 camcorder is not switched on or off in the traditional manner but by 40-60 ms long pulses. One pulse switches the camera on and the next one switches it off. Manual operation with a switch is virtually impossible to achieve. However, the timer described here offers a solution.
The timer generates the pulses automatically; the interval between two pulses can be set between about 1 s and 10 s. It operates from a 9 V (PP3 or 6F22) battery: the current drain is only 330 μA.
When switch S1 is closed (signal A – see Fig. 2). differentiating network R2-C1 ensures that IC2a receives only a short pulse (signal B), even if S1 remains closed for some time. Assuming that the circuit was quiescent before S1 was closed. pin 1 of IC2a is high so that the output of the IC (signal C) goes low as a result of signal B. The output signal of 1C2a triggers monostable IC1a via AND gate D2-D3-R3, whereupon the output of IC1a (signal E) switches on transistor T1. This transistor serves as the stop/start switch of the camcorder; its drain and source are connected to the camera.
At the same time that IC1a generates the start pulse. IC1b is triggered to commence measuring the time interval between the start and stop pulses. This interval can be preset with P1. During the interval, signal H is kept low and this disables switch S1. Once the mono time of IC1b has elapsed, signal H goes high via IC2d, so that IC1a is triggered a new and sends a stop pulse to the camera. The circuit then returns to the quiescent state until S1 is closed again.
As drawn, the circuit is particularly suitable for adding titles to the filmed material. One touch on S1 and the title in front of the camera lens is recorded within a few seconds.
Switch S1 may be replaced by an interval time for making speeded-up recordings.
