Function generator sync output at twice the frequency?

[patrickl]

Hi everyone,

I'm trying to trigger a camera with pulses from a function generator. Currently the FG's sync output is connected to the camera input and gives a 50% duty cycle square wave equal to the frequency of the normally-outputted waveform (in my case, this is a triangle wave). I can trigger the camera to take pictures just fine with this setup.

Now, I am trying to capture TWICE per period of this triangle wave with this camera (once on the rising edge of the square wave trigger pulse, once on the falling edge). However, I cannot seem to do this even when I tried using BOTH of the camera's input pins and inverting one of them; it causes some sort of conflict.

Might there be a way to get the sync pulse of the FG to be TWICE the frequency of the normally-output waveform (triangle wave)? This would be a lot easier than making a frequency doubler/divider circuit (I don't have much electrical/electronics engineering experience and can't seem to find any/many off-the-shelf that work at low frequencies!). I've tried the modulation, sweep and burst features but may not have been using them correctly.

If it makes a difference, I'm using is a Marlin AVT machine vision camera (400Mb/s bandwidth), a Stanford Research Systems DS345 Function Generator, and am driving the trangle wave at 15Hz (Thus I wish to capture at 30Hz with the camera and wish to remain synchronized to the FG's clock).

Thank you,
P

 

[Timescope]

Two square waves from one triangular wave

Hello Patrickl,
Here is an idea that may require amplification of the triangular wave to work.
1. Use a diode and capacitor to store the positive peak of the triangular wave.
2. Do the same for the negative peak.
3. Use two comparators to compare the triangular wave with the peak voltages stored in the capacitors . Configure the comparator inputs so that the output is positive when the triangular wave exceeds the stored peak voltage ( it will, because the capacitor voltage is one diode drop below the tip of the triangle)
4.Use a zero voltage switch that produces a positive pulse when the triangular wave is at zero volts.
5. OR gate the three outputs above and use the output of the OR gate to drive a toggle flip flop (D or J-K). The output of the flip flop will be twice the frequency of the triangular wave.
To understand the idea, draw the three waveforms like a timing diagram.
Please note that further refinements to the circuit are required to take into account the common mode range restrictions of the comparator, voltage levels etc.
Timescope.

 

[Harald Kapp]

Can you live with a rectangular output instead of the triangular one?
Then: set the function generator to twice the frequency you need. Sync the camera with that freqeuncy from the scnc output. Use a flipflop to divide the freqeuency by 2 for the functional output. Thus the functional output is still the same frequency as befor but the sync is twice as fast.

 

[KrisBlueNZ]

So your camera triggers on one edge (say the rising edge) of your squarewave but not on the falling edge, and you need to produce a signal that triggers the camera on BOTH edges of the squarewave?

A simple way is to convert both edges into pulses of much shorter duration than the squarewave and combine the positive and negative pulses. A simple resistor-capacitor "differentiator" (capacitor in series, resistor to ground) will convert a rising edge into a shorter pulse. There are various ways to combine the two pulses.

If your camera is fully floating with respect to the function generator, you can use a bridge rectifier to convert the negative pulse to positive. Or you could use two optocouplers. There are LOTS of ways to do this.

Alternatively you could use two monostables made from a 556 and trigger the two sides from opposite edges of the waveform (by supplying an inverted copy of the squarewave to one of the monostables) and diode-ORing the monostable outputs together.

I tried to think of as many simple ways as possible to do what I think you want. Here is the result:

If you think I understand you, and if any of these ideas sound like what you're after, tell me more about the characteristics of the function generator's square wave output and the camera's trigger input, and which ideas appeal, and I'll put some numbers onto a schematic.