A help circuit for camera triggering with Microcontroller:
Two Step Trigger TST01.

Built at: Jan.20.2001 Last update: Dezember 06, 2004

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Problem:
With many point and shoot cameras, SLR´s and also digitalcameras (see my SONY DSC 505 Cybershoot) 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 accoustic 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 triggerdelay. 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 can´t 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 microcontroller 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 microcontroller. With the eight switches I can adjust the servomovements and the measuringtime for different KAP-Rigs and cameras. The LED´s D1 and D2 show the timing. D1 is switched on in the MEASURING position, D1 and D2 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 soldert at first, because they are mounted under the IC-Socket.

Function of a four channel remote control:
The transmitter always produces four pulses wich are transmitted by the antenna. The time of these pulses are proportional to the movement of the controlstics. They are 1 ms to 2 ms in time. If the stic is in the middel, at the neutral position, the impulstime 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 addet. This delay with no pulses is used to syncronize the transmitter and the receiver. After the delay, four new pulses are generated, proportional to the position of the stics. The repeatingtime of this four pulses is approx. 20 ms, but with 40 ms it also will work.

Pulses of a four channel transmitter. On top you see the four pulses for the four channels (servos). At the bottom there is one signal for one servo. This signal is proportional to the position of the controlstic in the transmitter and can be 1 - 2 ms in time. After 20 ms the transmitter produces four new pulses.

Solution with a microcontroller:
The TST01 is plugged between the receiver and the trigger-servo. It always controls the impuls from the receiver. If this impuls is longer than 1,7 ms it means the KAPer wants to trigger the camera. To prevent any transmission-errors this impuls (1,7 ms) must be there for at least 0,5 sec to trigger the camera. The microcontroller then generates new pulses for the triggersevomovement in two steps:

Test circuit of the TST01. Here I can change some components to test the function. The pulses from the transmitter are generated with a servotester.

Triggering: First step:
The servo moves from the NEUTRALPOSITION to the MEASURINGPOSITION and the camera begins with the measuring. The position of the servo, that triggers this function of the camera can be adjusted with three DIP-switches at the TST01 in 8 steps. After that there is a short delay so the camera can do its job. This measuringtime is different at different cameras and can be adjusted with two switches from 2 to 3,5 sec in four steps.

Triggering: Second step:
When the measuringtime 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, too. In this position there is a short delay of aprox. 0,5 sec. After that, the servo moves back to the NEUTRALPOSITION.

Now the picture is taken. The camera needs time to store the picture in memory and the flash must be loaded again. So there is a triggerstop for aprox. 7 sec. now. After that time the cameratrigger is "sharp" again, the LED´s are flashing and the next picture can be shoot.

Additional function:
The camera has an auto-switch-off-timer, which switches the camera off, when it is not operating for more then 3 minutes. If the camera is in the air and the KAPer has to do something other, it can happen, that this time runs out and the camera switches off. The KAPer doesn´t need this function. If the KAPer doesn´t trigger the camera or there are errors in the transmissionline, the TST01 generates a measuring movement of the triggerservo after a while to prevent a camera time out "error". With this function the camera doesn´t switch off because the timer in the camera is started new, if the camera is measuring.

Technical solution:
The main components in the electroniccircuit are a PIC16F84 - Microcontroller from Microchip, a 4 MHz crystal, two LED´s, a DIP-switch and some other parts. The servopositions and the measuringtime can be adjusted to the Rig and the camera with the DIP-switch. The LED D1 lights if the servo is in the MEASURINGPOSITION, D1 and D2, if the servo is in the TRIGGERPOS.

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: MEASURINGPOSITION of the servo, low bit S4: MEASURINGPOSITION of the servo S5: MEASURINGPOSITION of the servo, high bit S6: TRIGGERPOSITION of the servo, low bit S7: TRIGGERPOSITION of the servo S8: TRIGGERPOSITION of the servo, high bit		The plan of the TST01 is very small because the microcontroller dosn´t need much external parts.

Building of the TST01:
If you have ever build an electronic circuit the building of the TST01 will not be a problem for you. If not, maybe a friend can help you.
At first there must be a layoutfoil. You can printout the layout and reduce it in the right size (see 40 mm) with a copymashine. Now you have a little sharp layoutfoil. With this foil you have to expose the circuit board. After that, the circuit board must be developed and etched.

The finished circuit board must be drilled (0,8 mm) and filed to the right measurings. After the mechanical work is done you have to add the components to the circuit board and solder them. Don´t forget the small wirebridge. Attention: The two 33pF condensers must be addet at first, because they are mounted under the IC-socket.
The microcontroller should be plugged in an IC-socket. The PIC16F84 is built in a 18 pin DIP-case. 18 pin IC-sockets are not easy to get, so I have used a 20 pin socket. You have to look at the right position of the controllerchip: It must be plugged to the left end of the socket. The two pins on the right site of the socket are not used.

Circuit board of the TST01. You can print out this layout, reduce it in the right size with a copymashine (40 mm) and use it to expose the circuit board. The layout is mirrored so that the layerside comes to the top of the circuit board. This reduces an underlight at the exposing and the ready circuit board is very sharp.
Mountingplan of the TST01. You have to look at the position of the 18 pin microcontrollers in the 20 pic IC-socket. It must be plugged to the left end of the socket. The two pins on the right site of the socket are not used. Don´t forget the wirebridge. There are no plugs for the servo and the receiver. You must solder some wires to connect the servo and the ceceiver because the different remote control systems have different connectors.

Programming:
Who is interested at this software can get in touch with me by mail. I will send you the assembler sourcecode "tst01-h.asm" by e-mail.

The biggest problem will be the programming of the microcontroller. There are different solutions:

1. If you have a friend, ho hase the needet software and a pic-programmer you only have to assemble the sourcecode and programm it into the controllerchip.
2. In the WEB there are many plans to build a pic-programmer for the PIC 16F84. This easy devices often can only programm one type of PIC´s, but they are very low in price and easy to build. Have a look at my surfers guide.
   You can get the Assembler to translate the sourcecode at the Microchip Homepage.
3. If you are interested on programming the PIC-controllers you can get the Microchip starterset. There is everything you need to devolope a programm and "burn" it into a microcontroller. There is a editor, a assembler, a very good debugger and of course the programmer hard- and software. With this starterkit you can programm many different types of PIC-controllers. The two CD-ROM´s are filled with software, data sheets, examples and so on.

Partlist:

Test and adjust the TST01:
The circuit is designed for use with 4,8V.
If the circuit is ready built and the controllerchip is programmed well and plugged into its socket the circuit can be tested.

If you have a power supply you can do the first try with this and look at the current of the device. The two LEDs are flashing for a short time to say that the circuit is going to work. It is the "readysignal". If there is no servo the current will be approx 3 mA without any LED and approx 20 mA if both LEDs are on. If this first test is good you can test and calibrate the TST01 at your receiver with Rig and camera.

For the first time all DIP-switches are set to 0. Switch on the power and the two LEDs flicker for a short time, the "readysignal".

If you move the controlstic at your transmitter now, the two LEDs show the two functions MEASURING (D1) and TRIGGER (D1 and D2). A plugged servo moves only a little bit in two steps.

Now you can adjust the servomovement for the MEASURINGPOSITION with the switches S3 to S5. Switch them into that position, so that the camera does the measuring but not the triggering.

After that you have to adjust the measuringtime with S1 and S2 to the need of your camera. You can choose times from 2 sec. up to 3,5 sec. in four steps.

At least switch the DIP-switches S6 to S8 to adjust the servo in the pos TRIGGER.

Possible devolopments for the future:
You can leave the DIP-Switch and program the TST with a programming-switch and a programming-led. The programmed positions and timings can be stored in the EEPROM of the PIC - controller. Then the device can be much smaller and all times which are not programmable in this version (TST01) can be adjusted.
Future??


Enjoy building the TST01 and of course enjoy KAPing with the Two Step Trigger.

Links to other KAPers and more you can find in my Surfers Guide.

I like to be available for questions, suggestions or experience exchange.

I would be very pleased about an entry in my visitor's book.

Manfred
http://KAP-Man.de

Manfred