Serial Cable for Camera
I needed a serial cable to link MaximDL to my D5000 camera. Here it is !
Because it is not possilbe to make the following scheme (http://www.beskeen.com/projects/dslr_serial/dslr_serial.shtml) because of the new TTL level used by USB-to-TTL adapters, I had to work a litthe bit to understand what was wrong and what I needed to update.
The programmes controling the camera (such as MaximDL) start with RTS at 0 and trigger the shitter with RTS set to 1.
With the older voltage levels, they are starting at -6 volts and openning the shutter with a +6V (cf. scheme on link above, you will understand the PNP switch and the diode to delete the negative part of the signal).
With the new voltage levels, the same sequence gives a 3.3V then a 0V. If we do not adjust the electronic, the result is absolutely the converse that we are expecting !
To cope with this issue, I just:
* adapted my FTDI USB-to-TTL adaptor which was giving 5V, RTS and ground (and other useless things such as TX, RX...) --> the 5V has been replaced with the 3.3V ;
* added to the original scheme a not gate, my only goal was to have a voltage on my PNP collector higher than the 0.7V needed to saturate the NPN ;
* I remove the diode which is now useless in absence of negative signal voltage.
I tried and tested the prototype which gave good results !!
I hope it will help someone !
RS 232 Voltage levels
In order that the RS 232 transmitters and receivers can be designed to a common standard, it is necessary to define the voltage levels that constitute the two logical states required for data transmission. The two states are defined as in the table below.
|Signal Voltage levels Volts||Logical State|
|-3 to -25||1|
|+3 to +25||0|
It is also necessary to define the voltage states for the control signals as these are widely used within RS 232.
|Control Voltage levels Volts||Logical State|
|-3 to -25||OFF|
|+3 to +25||ON|