![]() but you can hack it (open DB9 cover and replace it with larger one so your TTL shifter fits in). They are all low power devices that will have hard time powering external circuit (unless circuit is very low power). i didn't check how much current one can get out of RS232 port on a newer computer but i bet it is much less. nowdays with energy saving, low power devices etc., you are lucky to see +/-5V. In the old days PCs used internal +/-12V supply to power ports (and provide enough juice that could be stolen, I was getting some 25mA from my oldest PC). RS232 spec says that proper signal for "0" is +3.+25V and "1" is -3.-25V. search for simple PIC programmers that ware stealing power from port and you will see that while they can work, this is the most common problem when they don't work. you expect that circuit to provide enough power to run another such circuit. now the PC software that communicates with the camera need to take control over handshaking lines and force them into particular state(s) to produce those signals.īut think about it, one such circuit is already in your PC. by switching these lines, one can produce signal that can be used to power devices. port has few handshake lines which are sometimes not used (none of the three circuits you posted uses them). stealing power from port is simple enough. ![]() while it can work, it is not something you want to rely on, specially that RS232 ports are endangered species, most new computers don't even have them and those that do are increasingly moving to low power (les power can be stolen from port). Stealing power from port is not a good idea. you can modify it by adding optocouplers (you can get version that has TTL driver output, not just transistor). your first circuit is NOT optically isolated. if your camera is not battery powered (uses power supply) and PC is also connected to AC (not a laptop running on batteries), you could use optical isolation.ītw. if your camera is powered from battery, you won't need this (it sure doesn't hurt). Optical isolation is used when circuits are powered from different supplies. In addition I understand from this that a suplimentary power source must be added to the camera side.Īny suggestion is very appreciated. Opto Isolator 2 is more complicated because I have just the picture of layout. How can this be put in practice? How can I make the adaptor using just the power from PC and camera? Positive supply is derived from RTS and negative one from the DTR line, therefore it is necessary for the user program to set the RTS status to logic zero & DTR to logic one in order to get the proper supply levels at the output. "Power to the PC side of the circuit is derived from the signal lines DTR and RTS. But the power supply is giving me hard time. Opto Isolator 1 seems to be the most convenient, I have the PCB diagram, component layout, component list and most important I can order the PCB very cheap. I found 2 diagrams using optocouplers but I don't know how to use them. That's why I tried to build an opto-isolator. So far it works, but it doesn't provide protection. I've read that camera uses TTL signals, while serial PC port uses +/-12V.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |