Sensor connection

[erniehatt]

thanks again Ron,
I assume the resistors will be as per the original schematic. If so no need for reply.
Certainly will keep you informed on the out come, should not be too long, designing a board incorporating the laser circuit as we speak. Ernie

 

[erniehatt]

Hi Ron,
Been browsing those truth tables again, NO I haven't found a problem with the circuit, what I have found is we could have gotten away with a M74HC4078 NOR Gate

A B Q
0 0 1
0 1 0
1 0 0
1 1 0
Truth Table

Being as I have the parts on order and have designed a board I will try yours out, from what I see I have no doubts it will work. Ernie

 

[Reloadron]

Yes, could have used it. No shortage of gates out there.

I just went with a gate I was a little more familiar with. There are likely 1/2 dozen combinations of parts that would work. Hope you had a good weekend....

Ron

 

[erniehatt]

Ron, weekend was pretty boring really, couldn't do much, raining.
will hopefully get the parts tomorrow, don't have an electronics supply outlet near by, so have to send away for them.
I hope you didn't think I was knocking your choise, far from it, I very much appreciated the help you gave, as you say there must be a lot of combinations you can use, so which one matters little. Ernie

 

[erniehatt]

Ron, Set up your circuit, with a couple of switches, triggered the Camera, but there seemed to be quite a sizable delay before it happened, had to hold the switch on for quite sometime before it triggered, this could be the switched what do you think. Ernie

 

[Reloadron]

The transition should be just about instantaneous, that is strange. Place a meter where the camera trigger would be sans camera. When the button is hit the transition high to low should be instant. We don't have anything in there that should induce a delay. This is where a scope would be nice but the meter should provide a good idea.

Ron

 

[erniehatt]

Ron,
I finally got it sorted, I had to tie the resistors low, and had to tie a resistor low on the output, but it did trigger the camera pretty quick in the end. Would this setup have any detremental effects. I made the board and soldered all components today, just have to fit sockets, still waiting for PT's coming from your neck of the woods. Thanks Ernie

 

[Reloadron]

Hi Ernie

Should work just fine. Let's hope your subjects cooperate.

Ron

 

[erniehatt]

Thanks Ron,
The subject matter is another problem to get over, the little buggers are not overly co-oppretive at the best of times, probably be more of a problem that building the module. I will let you know how it goes. thanks again for the help. Ernie

 

[erniehatt]

I haven't set this up with laser and light sensor, have been waiting for the sensors to arrive did that today, just tried it with a couple of switches, i am getting a small responce on the multimeter but not on the camera trigger. Could this be because of the switches, if not how can I fix it, would a small preamp make a difference. Ernie

 

[Reloadron]

Hi Ernie

I forget, which sensors did you go with for sensing the LASER?

Ron

 

[erniehatt]

G-day Ron, hope everything is treating you well.
The PT's I have are BPW77N from Vishay. I have used them with lasers before the work ok. Here's a data sheet. Ernie

 

[erniehatt]

Would these generate enough output to activate the trigger. Ernie

 

[Reloadron]

Hi Ernie

Sorry I have been slack. Those should work but I can't figure out why plan A isn't triggering the camera? I keep thinking as to what the hell am I not seeing or missing. The photo transistors need only trigger the gate. Then we trigger the camera by placing the trigger pin low? What am I not getting?

Ron

 

[erniehatt]

No problem Ron, the circuit works, I put the DMM on the output and it is triggering, but the signal is not being picked up by the Camera trigger, perhaps the signal is not strong enough, your guess is as good as mine. I have only tried this using a couple of switches as your diagram, will the PT's make a difference to the signal strength. One other possibility is, that if I use a single PT on the trigger I have to fix two 10k resistors to the negative lead. one going to ground the other to the trigger input, would I need to add something of this nature. Ernie

 

[Reloadron]

This is my thinking, maybe we need a transistor to drive the camera. Let me look at the circuit we have and make a suggestion or two tomorrow. We do have camera ground tied to our circuit ground correct? Hopefully tomorrow at work will be quieter than it has been and I can look at things.

Ron

 

[erniehatt]

Ok Ron, yes the ground is connected. After reading your thoughts on a transistor I did some experimenting. I added a fast triggering SCR to the out put, and I did manage to get the camera to trigger. But came up with another problem, I am getting a high on the output, not that that is bad as I can trigger on either, I am using only two switches, and they are both giving different strengths of signals at the output, this makes it impossible to set a threshold, Ernie

 

[Reloadron]

Attached is a mod that should work. We come right off the gate and drive the transistor that is across the cam trigger line and common. We eliminate the inverter on pin 8 and go right to the transistor. A 2N2222 or 2N3904 or just about any common switching transistor should work.

The photo switches should have about the same output for the same amount of LASER light striking them.

Ron

 

[erniehatt]

Thanks Ron will give it a go tomorrow. Ernie

 

[erniehatt]

Hi Ron, I am in the process of making a circuit board for this, one question, would I just send unused pins direct to ground, or through a resistor. Ernie