cxsparc? Sonia slave+RF603c flash trigger mods?

Started Mar 18, 2012 | Discussions thread
OP RussellInCincinnati Veteran Member • Posts: 3,201
amazing, your circuitry suggestions worked immediately

Success. Following forum member Cxsparc's instructions, a $16 dollar Sonia Digital Slave Unit

can, if modified by adding a transistor and resistor inside its case, activate through its hot shoe a Yongnuo RF-603c or RF-603n wireless flash trigger.

For this to work, the Yongnuo radio transceiver that is slid into the top of the Sonia Digital Slave, must itself have a resistor added inside its case, in order that it configure itself as a transmitter. Unmodified Yongnuo radio transceivers, plugged into remote flash units within 50 meters or so, will automatically react as receivers to signals from the modified transceiver. Too bad that the inexpensive Sonia digital slave unit doesn't supply a special "TTL wakeup signal" through its hot shoe, to make an attached Yongnuo transceiver automatically realize it should be a transmitter. That's OK, we can rewire the Yongnuo to permanently be in transmitter mode.

The modification necessary to the Yongnuo transceiver to make it a transmitter, is to add a tiny 20 cent (Radio Shack sells 5 for about a dollar) 1/8th watt resistor of about 120000 ohms, connecting (i.e. soldering) one end of the resistor to the "J6" contact inside the Yongnuo disassembled casing. The other end of the resistor is easily soldered/connected to the Vin battery power terminal on the Yongnuo exposed circuit board. Make sure to cover the bare resistor leads with a bit of electrical tape or heat shrink tubing to make sure the bare leads don't touch anything inside the case after reassembly. The resistor is so small that the casing will easily reassemble.

A modified transceiver will, when turned on, always light up both its green LEDs full time, showing that it is functioning as a flash-signal transmitter. In contrast, unmodified Yongnuo transceivers that are not in the presence of a transmitter will automatically power up with a single green LED lit, showing they are receivers. Actually unmodified transceivers will automatically power up with both LEDs glowing green, if they are turned on while in range of the active transmitter. The receivers' second LED being lit shows that they are in good radio contact with a transmitter. Then press the "test" button on the powered-up transmitter, and nearby, active receiver LEDs will flash red, and whatever flashes are plugged into those receivers will fire.

The modification necessary to the Sonia Digital Slave Unit, it make it capable of firing the ultra modern Yongnuo wireless radio triggers, is to open it up and connect/solder in a transistor and resistor. The transistor is a BC550 or 2N3904. My 2N3904 came from Radio Shack for $1.19 (buy two in case you mess up the first one). The 1000 ohm, 1/8th watt resistor is also from Radio Shack, again about 1 dollar for 5. You should of course have a grounded 15 watt soldering iron, and thin rosin core solder, at the ready.

The "emitter" wire of the tiny transistor must be connected\soldered to some bare metal place on the blue wire inside the Sonia case. The "collector" wire of the tiny 3-wire transistor is connected to the red wire inside the Sonia case. The middle "base" wire of the transistor is connected to one end of the 1000 ohm resistor, then the other wire from the resistor is in turn soldered to the bare "left-hand" wire of the red LED. The red LED wire is "on the left" if you are looking down at the circuit board in your hands, with the red LED pointing towards your chest.

When the bare wires are wrapped in a bit of insulating tape and the Sonia case is reassembled, the red LED on the Sonia case will no longer light up under any conditions. But that's OK, because surprisingly, when you slide the Yongnuo RF-603x transceiver into the Sonia hot show and turn the Yongnuo on, one of the Yongnuo LEDs lights up whenever the Sonia LED would have lit up. That is to say, the Yongnuo red LED duplicates the Sonia's LED behavior whenever it's attached to the Sonia's output hot shoe, making it OK that our transistor modification snuffed out the Sonia's internal LED.

And that's it for the modifications. To use, turn on the Sonia digital slave unit, and press the "Program" button to the down position, and fire the Nex 5's preflash-plus-flash towards the Sonia black optical sensor. Then push the Program button again on the Sonia, it will spring back up to the "up position". Now you can turn the Sonia off with its switch and wait a 10 seconds. Now the Sonia has been programmed to "remember" the Nex pre-flash pattern.

Then attach a modified-to-be-transmitter $20 dollar Yongnuo RF-603c or -n radio transmitter into the Sonia hot shoe. With both the Sonia and the Yongnuo turned on, you are armed and ready. The Nex 5 flash, when fired, will activate the Sonia digital slave unit only on the final flash, which will in turn activate the Yongnuo transmitter, which will in turn fire any number of Yongnuo RF-603x transceivers (and their attached flashes) that are "listening" in the area. Of course if the flashes being fired have built-in optical slaves, their optical slave functions must be turned off, because you are intending that those flashes only fire when they are attached to Yongnuo transceivers( that are acting as flash trigger receivers).

But how do you have the Sonia digital slave unit "see" the Nex 5 flash, but not have the Nex 5 flash "show up" in the picture? I have found it adequate to go into the Sony menu, under brightness, and turn the flash fill EV setting to -2, the minimum, making it quite weak. I also have taped a bit of aluminum foil over the flash, so that the flash only illuminates "upward" instead of forward. One can even put a balloon over both Nex flash and slave triggers so that only the triggers see the flash.

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