BushSnake
New Member
Hi all
I've got a little private project going that requires an IR beam for a trigger, and will be used as a portable device in an outdoor environment. It has to be sensitive to be triggered by the a piece of wire being waved through the beam at relatively high speeds, and this section of the system has to be done on analogue components only. This sounds fairly simple, but I'm having a lot of trouble getting the system to work on variable distances, and especially in direct sunlight. I've worked on a couple of designs but it seems like I'm doing something wrong as this kind of thing must have been done in the past and it can't be that difficult.
My problem is as follows: From what I've worked out I need a variable resistor to determine the biasing of the photo-transistor. Based on some initial trials, the value of this resistor needs to be between 1k and 10M, depending on the distance between the sending and transmitting units of the IR system (i.e. the amount of light entereing the photo-transistor). But I'm battling to design a voltage controlled resistor circuit that will do this for me. I've attached the circuit diagram of my design... so please comment on that?
I've also attached the complete circuit necessary to return a 0 or 5V from an IR beam break. Please feel free to give other design ideas, or to comment on the design? I can't claim to be the world's best circuit designer... which is why I'm asking some gurus on this forum! I've looked at a number of designs on the web, and elsewhere on this forum, but I still can't find a design that I'm happy with.
Thanks in advance
Andre
I've got a little private project going that requires an IR beam for a trigger, and will be used as a portable device in an outdoor environment. It has to be sensitive to be triggered by the a piece of wire being waved through the beam at relatively high speeds, and this section of the system has to be done on analogue components only. This sounds fairly simple, but I'm having a lot of trouble getting the system to work on variable distances, and especially in direct sunlight. I've worked on a couple of designs but it seems like I'm doing something wrong as this kind of thing must have been done in the past and it can't be that difficult.
My problem is as follows: From what I've worked out I need a variable resistor to determine the biasing of the photo-transistor. Based on some initial trials, the value of this resistor needs to be between 1k and 10M, depending on the distance between the sending and transmitting units of the IR system (i.e. the amount of light entereing the photo-transistor). But I'm battling to design a voltage controlled resistor circuit that will do this for me. I've attached the circuit diagram of my design... so please comment on that?
I've also attached the complete circuit necessary to return a 0 or 5V from an IR beam break. Please feel free to give other design ideas, or to comment on the design? I can't claim to be the world's best circuit designer... which is why I'm asking some gurus on this forum! I've looked at a number of designs on the web, and elsewhere on this forum, but I still can't find a design that I'm happy with.
Thanks in advance
Andre