A help circuit for camera triggering with Micro controller: Two Step Trigger TST01 - page 1

Problem:
With many point and shoot cameras, SLRīs and also digital cameras the triggering is in two steps. At first you press the trigger button only a little and the following happens: The camera is measuring the object, the light and the distance. After a few seconds, when the camera has finished, there is an optical and an acoustic signal. Now you can press the trigger down, and the camera triggers. This is the course at any time you press the trigger. That means, there is always a trigger delay. If you want to trigger the camera with the servo in your KAP-Rig you have the problem to trigger the camera in this two steps. You canīt press the button only a little, wait at any signal and press the button down then. There are different solutions for this problem. I have built an electronic circuit with a micro controller that always triggers the camera in two steps.

The Two Step Trigger TST01. The ready built circuit of the TST01 is only 28 x 40 mm in size. It is plugged between the receiver and the trigger servo. At the left side you see the micro controller.
With the eight switches I can adjust the servo movements and the measuring time for different KAP-Rigs and cameras. The LEDīs LED 1 and LED 2 show the timing. LED 1 is switched on in the MEASURING position, LED 1 and LED 2 are on in the TRIGGER position.



There are only a few parts and a small circuit board needed to build the TST01.

Attention: The two little 33pF condensers must be soldered first, because they are mounted under the IC-Socket.

Function of a four channel remote control:
The transmitter always produces four pulses which are transmitted by the antenna. The time of these pulses are proportional to the movement of the control sticks. They are 1 ms to 2 ms in time. If the stick is in the middle, at the neutral position, the pulse time is 1.5 ms. The receiver receives these pulses and passes them to the four servos. When all four servos have been served, a delay is added. This delay with no pulses is used to synchronize the transmitter and the receiver. After the delay, four new pulses are generated, proportional to the position of the sticks. The repeating time of these four pulses is approx. 20 ms, but [as much as] 40 ms it also will work.

Pulses of a four channel transmitter. On top you see the four pulses for the four channels (servos). [Ed-this is the signal from the Transmitter, the receiver separates the four pulses and sends them to the appropriate channel] At the bottom there is one signal for one servo. This signal is proportional to the position of the control stick in the transmitter and can be 1 - 2 ms in time. After 20 ms the transmitter produces four new impulses.

Solution with a micro controller:
The TST01 is plugged between the receiver and the trigger-servo. It intercepts the pulse from the receiver to the trigger servo. If this pulse is longer than 1.7 ms it means the KAPer wants to trigger the camera. To prevent any transmission-errors this pulse (1.7 ms) must be there for at least 0.5 second to trigger the camera. The micro controller then generates new pulses for the trigger servo movement in two steps: Test circuit of the TST01

Here [Ed-on the breadboard in picture to the right] I can change some components to test the function. The pulses from the transmitter are generated with a servo tester.

Triggering: First step:
The trigger servo moves from the NEUTRAL POSITION to the MEASURING POSITION [Ed-shutter button partially depressed] and the camera focuses and measures light for proper exposure. The position of the servo that triggers this function of the camera can be adjusted with three DIP-switches on the TST01 in 8 steps [S3, S4, S5]. After the servo moves to the Measuring Position there is a short delay so the camera can do its job. This measuring time is different for each camera and can be adjusted with two switches from 2 to 3.5 sec in four steps. [S1, S2]

Triggering: Second step:
When the measuring time is over the servo moves to the second position, TRIGGER, and the camera triggers. This position can be adjusted with three switches in 8 steps. [S6, S7, S8]   The TST01 will hold the trigger depressed for aprox. 0.5 sec. After that, the servo moves back to the NEUTRAL POSITION.

Once the picture is taken. The camera needs time to store the picture in memory if it is a digital camera, or advance the film if it is a film camera, and the flash must be recharged. So there is a 7 sec. delay built in before the camera can be triggered again. After that time the TST01 will accept another signal from the transmitter, the LEDīs are flashing and the next picture can be shot.

Additional function:
If the camera has an auto-switch-off-timer, which switches the camera off, when it has not operated for more then 3 minutes. [Ed-some digital cameras have the ability to switch this feature off] The KAPer doesnīt need this [auto-switch-off-timer] function. [However if you already own a camera with this feature] if the KAPer doesnīt trigger the camera or there are errors in the transmission line, the TST01 generates a measuring movement of the trigger servo after a while to prevent a camera time out "error". With this function the camera doesnīt switch off because the auto shut-off timer in the camera is started anew.

TST01 Schematic Technical solution:
The main components in the electronic circuit are a PIC16F84 -Micro controller, a 4 MHz Quartz [crystal], two LEDīs, a DIP-switch and some other parts. The servo positions and the measuring time can be adjusted to [accommodate] the Rig and the camera with the DIP-switchs. The LED D1 lights if the servo is in the MEASURING POSITION, D1 and D2, if the servo is in the TRIGGER POSITION.

With the 8 DIP-switches the TST01 can be adjusted to the Rig and the camera.
S1: Measuring time low bit
S2: Measuring time high bit
S3: MEASURING POSITION of the servo, low bit
S4: MEASURING POSITION of the servo
S5: MEASURING POSITION of the servo, high bit
S6: TRIGGER POSITION of the servo, low bit
S7: TRIGGER POSITION of the servo
S8: TRIGGER POSITION of the servo, high bit
The plan of the TST01 is very small because the micro controller doesnīt need many external parts.