How To Trigger Two Wireless Transmitters From One Camera Hot Shoe

Thread Starter

gebseng

Joined Nov 24, 2017
35
Hi everyone,

A seemingly simple problem: As you might know, all that a photo camera's hot shoe does to trigger a flash is to close a switch when the camera release is pressed. The flash itself, mounted on the hot shoe, has a circuit with approx. 3V, and the flash fires as soon as the switch is closed.

Now, I have wireless transmitters (which are triggered much like a flash) that go into a camera's hot shoe, and I need to trigger two of them at the same time



My first though was: easy enough, I'll just use one of these dual hot shoes to mount the two transmitters on my camera:


But, it didn't work. Sometimes, just one transmitter was triggered; sometimes none at all.
Next, I tried to wire a setup myself, like this:




But the effect was the same: just one remote was triggered fine, but not two.

So, can you explain why this setup doesn't work?

Thanks for your input,

geb
 

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MrSoftware

Joined Oct 29, 2013
2,012
Can the transmitter pair with only a single receiver? It seems the easiest solution, if possible, is to pair 2 receivers to the single transmitter. Surely this has been done before?

Are you sure the shoe only gives a simple on/off signal, no data is being transmitted?

If you cannot pair 2 receivers to your transmitter, and the dual-shoe setup would be a solution if it worked; then maybe your current shoe just cannot provide enough current to control 2 devices. One possible solution is add a 3v regulated power supply and use a pair of MOSFETs (one n-channel and one p-channel) to control the +3v line. Connect the n-channel gate to your shoe + line. Use a pull-up resistor to keep the p-channel gate high (which will keep the p-channel turned off) and use the n-channel to pull the p-channel gate low, so when the shoe triggers the n-channel will turn the p-channel on. I explained that really badly, did it make sense?
 

Reloadron

Joined Jan 15, 2015
5,913
What camera do you have as all camera hot shoes do not have the same pin out configurations. I know my Canon EOS 10D or 7D are not like what you posted. I also have remote IR signals and slave flash so this all comes doen to what you have and what you are trying to do?

Ron
 

Thread Starter

gebseng

Joined Nov 24, 2017
35
Can the transmitter pair with only a single receiver? It seems the easiest solution, if possible, is to pair 2 receivers to the single transmitter. Surely this has been done before?

Are you sure the shoe only gives a simple on/off signal, no data is being transmitted?

If you cannot pair 2 receivers to your transmitter, and the dual-shoe setup would be a solution if it worked; then maybe your current shoe just cannot provide enough current to control 2 devices. One possible solution is add a 3v regulated power supply and use a pair of MOSFETs (one n-channel and one p-channel) to control the +3v line. Connect the n-channel gate to your shoe + line. Use a pull-up resistor to keep the p-channel gate high (which will keep the p-channel turned off) and use the n-channel to pull the p-channel gate low, so when the shoe triggers the n-channel will turn the p-channel on. I explained that really badly, did it make sense?
Thanks for your input!

I need two transmitters, because only this setup allows me to control the power output of two studio flashes independently.

Yes, I'm pretty sure the hot shoe (same as a PC-sync jack) only closes a switch. I have very old purely mechanical camera, and they operate in the same way.

The hot shoe does not provide ANY current, it's just a switch.

best,

geb
 

Thread Starter

gebseng

Joined Nov 24, 2017
35
What camera do you have as all camera hot shoes do not have the same pin out configurations. I know my Canon EOS 10D or 7D are not like what you posted. I also have remote IR signals and slave flash so this all comes doen to what you have and what you are trying to do?

Ron
Thanks Ron! I have a Sony A7, but the basic functinoality of all hot shoes is the same - the middle pin and the metal mount are connected for a fraction of a second while the shutter is actuated. All additional pins around the middle pin allow TTL etc, but are not needed for the triggering process itself.
 

Dodgydave

Joined Jun 22, 2012
9,936
Hi everyone,

A seemingly simple problem: As you might know, all that a photo camera's hot shoe does to trigger a flash is to close a switch when the camera release is pressed. The flash itself, mounted on the hot shoe, has a circuit with approx. 3V, and the flash fires as soon as the switch is closed.

Now, I have wireless transmitters (which are triggered much like a flash) that go into a camera's hot shoe, and I need to trigger two of them at the same time



My first though was: easy enough, I'll just use one of these dual hot shoes to mount the two transmitters on my camera:


But, it didn't work. Sometimes, just one transmitter was triggered; sometimes none at all.
Next, I tried to wire a setup myself, like this:




But the effect was the same: just one remote was triggered fine, but not two.

So, can you explain why this setup doesn't work?

Thanks for your input,

geb
What happens if you link the two together like here, then short the wires together( not on the camera) , do they both fire?
 

ebeowulf17

Joined Aug 12, 2014
3,275
Could it be radio interference between the two devices? I wonder if different devices tune in to different frequencies, like radio/tv/cb channels, or if different devices from the same manufacturer might use the exact same frequency, and use messaging to address/ID the corresponding receiving device (like having multiple devices share an I2C or CANBUS line.) If it's the latter setup, then having two transmitters trying to transmit at exactly the same moment could result in noise that prevents either receiver from getting a clear signal.

I know very little about these transmitters - just brainstorming here.
 

ebp

Joined Feb 8, 2018
2,332
What do the DIP switches on the transmitters do?

I think it very likely that ebeowulf's analysis is correct - either RF conflict or data conflict. If the switches set RF frequency "channel" then setting them for the maximum difference might work.

Do the transmitters and receivers "pair" in some fashion or is this a simple transmitter talks receiver listens scenario?
 

Thread Starter

gebseng

Joined Nov 24, 2017
35
Could it be radio interference between the two devices? I wonder if different devices tune in to different frequencies, like radio/tv/cb channels, or if different devices from the same manufacturer might use the exact same frequency, and use messaging to address/ID the corresponding receiving device (like having multiple devices share an I2C or CANBUS line.) If it's the latter setup, then having two transmitters trying to transmit at exactly the same moment could result in noise that prevents either receiver from getting a clear signal.

I know very little about these transmitters - just brainstorming here.
Thanks for the idea, I tried several different channels, but to no avail.
 

Thread Starter

gebseng

Joined Nov 24, 2017
35
What do the DIP switches on the transmitters do?

I think it very likely that ebeowulf's analysis is correct - either RF conflict or data conflict. If the switches set RF frequency "channel" then setting them for the maximum difference might work.

Do the transmitters and receivers "pair" in some fashion or is this a simple transmitter talks receiver listens scenario?
There is no pairing, just selecting the same channel on sender and receiver, and then the receiver listens.
 

Thread Starter

gebseng

Joined Nov 24, 2017
35
What happens if you link the two together like here, then short the wires together( not on the camera) , do they both fire?
Wow, great idea! I just tried connecting "minus" of transmitter A with "plus" of transmitter B. Now, everytime I connect "minus" of transmitter B with "plus" of transmitter A, both flashes fire, works like a charm! Now I just have to implement this solution to the dual hot shoe,

best,

geb
 

Dodgydave

Joined Jun 22, 2012
9,936
Wow, great idea! I just tried connecting "minus" of transmitter A with "plus" of transmitter B. Now, everytime I connect "minus" of transmitter B with "plus" of transmitter A, both flashes fire, works like a charm! Now I just have to implement this solution to the dual hot shoe,

best,

geb
Ok so now they both fire, that sounds like they need a Voltage input to trigger them.

you need to see what pulse or output your camera gives out on the "hot shoe", then make a Slave trigger unit.
 
Last edited:

ebeowulf17

Joined Aug 12, 2014
3,275
Wow, great idea! I just tried connecting "minus" of transmitter A with "plus" of transmitter B. Now, everytime I connect "minus" of transmitter B with "plus" of transmitter A, both flashes fire, works like a charm! Now I just have to implement this solution to the dual hot shoe,

best,

geb
If I've read this correctly, you've wired the two slave units' hot shoe connections in series instead of in parallel. I don't think this was what @Dodgydave was suggesting.

I think he was simply suggesting you try taking the camera out of the circuit and shorting the wires manually. Some quick searching and reading reveals that many cameras no longer use mechanical contact switching, but use various forms of electronic switching now, and that many of them have voltage and/or current limits, so there may be cases where shorting the wires manually and allowing the camera to switch them will yield different results. (read the section labeled "voltages" in the wiki here.)

Anyway, regardless of what was meant or how you came to it, if you've found something that works, that's great!
 
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