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 !
Source: http://www.radio-electronics.com/info/telecommunications_networks/rs232/signals-voltages-levels.php
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 VoltsLogical 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 VoltsLogical State -3 to -25 OFF +3 to +25 ON