Sensor connection

[Reloadron]

Directly should be fine.

Unused Input pins that is.

Ron

 

[erniehatt]

Thanks Ron

 

[erniehatt]

Hi, I am getting embarrassed about all this, and must say getting nowhere fast.
I have put together and built a circuit board to suit, which I have checked that many times I lost count.
everything seems to check out except the output which is not changing. here are some readings from my DMM set on 20v.
1) with no sensors connected reading at the inputs of 7404 is at 1.08 and the output side is .15, the output of the 7430 reads 4.60.
2) with a sensor attached the readings at the input jumps to 4.93 the output changes to 1.4 there is a very slight change, but no reaction at 7430 output. where am I going wrong here, have I been supplied with faulty chips, not sure, I will try then on the breadboard. Ernie

 

[erniehatt]

Well Ron, please excuse me for being thick I think it may have finally sank in, at least I hope so.
I breadboarded the thing again, and got the result that worked, I didn't need the Transistor on the output. So I put it back into the circuit board, with the necessary adjustments, guess what no output again, then I woke up, the board is setup for 5 sensors, of which I had only connected, so according to the truth table with these all sitting on high the output would read high, by switching on the one single sensor, it would still read high, I would need all the sensors connected and switched on to get a low. the reason it worked on the breadboard, I had only the one set of pins connected. hope my logic is correct here. Ernie

 

[Reloadron]

I will draw the "Front End" (sensors) in a rough and tell you what to do with the unused pins later today, likely after work.

Ron

 

[Reloadron]

Hi Ernie

OK, took a few min here at work. Attached is an overview of what we should have. When the LASER is striking the photosensor(s) they will be in an ON state placing the input pins of the 7404 hex inverter at a logic low. Any unused 7404 pins should be tied to ground/common/logic low. Logic low for the 7404 should be below 0.8 volts. So in a normal state all the outputs of the 7404 sould be a logic high to the 7430 NAND gate. Since it is NAND the output should be low from the 7430. That will hold the transistor turned off.

When any input to the 7404 is interupted (beam broken) the corresponding output will go low from the 7404 to the NANG gate and the 7430 output will go high turning on the transistor and triggering the camera.

Ron

 

[erniehatt]

thanks Ron, I tried this with the breadboard, and it did not trigger in this setup, I had to tie the resistors to the ground, and connect the output directly to the trigger unit, this way worked, the signals I got laser off 1.08v at 7404 and with the laser on about 4.6. I will set up the sensors tomorrow, and see how it goes with them all in the on state, it's the only way to test it properly. let you know how it goes. I will try the above setup again as well. Ernie

 

[Reloadron]

Hi Ernie

The photo transistor section should look like the attached image. Looking at the data sheet they tell me in the dark the current is ablut 100 uA or less. When the LASER is striking it the current can be 15 mA (max). If we drop the series resistor to 500 ohms from 10K it may help but originally I was not wanting to run any current to speak of through the photo transistor. 500 Ohms would give us 10 mA of current when the photo transistor is on state.

Ron

 

[erniehatt]

Ron
This is the thing that concerns me, The way the sensors are normally connected to my trigger unit is the right hand sketch, connecting it your way does not work. I am making this to use it's own power supply, normally it would use the power from the trigger unit.
The left hand sketch is the way I got it working.
The current at 15ma is that too much, with 5 PT's that would amount to 75ma, the power unit I have added should be ok too 1 amp. Ernie

 

[Reloadron]

I don't get it. The circuit you are using with the NPN Photo Sensor is actually an Emitter Follower circuit. Taking the signal off the photo transistor emitter. The output will be the opposite of taking the output off the collector using a collector resistor.

When light is striking the transistor it will be on. That will place close to a logic high at the output. Close to because there will be the forward voltage drop of the transistor to subtract.

Also, before I forget, the 7400 series ICs used are 5 volt chips. They are designed for 5 volt power and TTL (5 volt) logic.

Ron

 

[erniehatt]

Ron,
I don't understand the reason, but that is the way all light sensors are connected to the trigger unit, any other way does not for some reason work.
The supply I am using is 5v.
I will make up a couple of boards using both methods, and see what happens, But first up I will get the PTs setup properly, so that all the pins can be made active. Ernie

PS. Ron,
tried you setup via the breadboard again, and by varying the setup in the camera trigger got it to trip the camera.
With the normal setup it was a no go again, don't know what the difference is, will have to find out.
The other trigger I built for the panasonic FZ50 worked fine, this is the one I am building the sensors for as it has the quickest responce time, where shutter lag is concerned. I am off to make up the board etc. thanks Ron let you know the outcome. Ernie