Creating a simple, secure, and small RF receiver/transmitter

Wireless & IoT
1

I’m searching for a wireless control solution for a special effect I have developed for the stage and I’m wondering if folks here could give me some pointers. The effect is a self-contained remote controlled blood delivery device that makes an actor bleed onstage. Here is the current system that I’m using: 12v 2 channel remote RF relay from Carl’s Electronics: http://www.electronickits.com/remote_control/rf2.htm

I’m firing a 12v Clippard solenoid valve that releases pressure from a small air tank at about 125psi. This system has been very effective for me (I’ve currently got 4 of them running in a Broadway show) but I want to reduce the physical size of my device and lower the power needs to 6v or lower. What I like about the current system is that I don’t get any cross signals; it’s operating in a theater just off of Times Square, in the center of possibly the most complicated set of RF signals on the planet considering the combination of overlapping theater control systems and a zillion taxi cabs constantly driving around. The chipboard I’m using is larger than I’d like and has much more functionality than I need. I want something that will be able to securely perform as a momentary switch at 6v or less with the smallest possible footprint.

Any pointers would be greatly appreciated.

Seán McArdle

Hero Props: Prop Design and Engineering

Twitter: @heroprops

646.734.2198

2

You can make such devices very small by using the nRF24L01+ with a suitable MCU. 3V operation is feasible.

3

This is something you wear; (receiver, +12vdc p/s, solenoid valve, air-tank, “blood” supply)? Just out of curiosity, what are you using to supply the +12 to the solenoid valve? How much “blood” does it store? At 125 psig; does this “blood” shoot out like a fountain? Can all 4 units be used at once; by 4 users? I looked quick at the website you posted with 2 channel rx and relays on board; I think a big size savings would be in a TO220 size power FET over the relay (and only channel) Sounds like a fun play to watch! Don’t know of any commercial available product though.

4

Yes, it’s worn by the actors, usually in the small of their back. I’ll go ahead and tell you the show, it’s called Bengal Tiger at the Baghdad Zoo, currently running on Broadway, starring Robin Williams. Robin is wearing one of the rigs in the first scene of the show, his character gets shot three times in the chest, so three spots of blood spontaneously appear after he’s “shot” by a gold plated Desert Eagle. To answer your questions:

-12v supply is simply a 9v and two AAs wired in series. They power both the board and the solenoid. Right now we go through 3 9vs and 6 AAs per performance, so that’s another reason I want to go smaller, so I can use a small rechargeable battery, for the waste factor, the cost, and the size. Biggest cause of power failure: bent 9v clips.

-about 14oz blood, in a Nalgene bottle flask.

-At 125 it can shoot like a fountain, but I have a pressure regulator in the system that takes the pressure down to between 30-50psi, depending on the effect.

-All 4 units can be used at once, but they aren’t at the moment. They do not interfere with each other at all, and in fact the remote transmitter/receivers can be swapped in case of failure, so each unit can be used as a backup for another.

Yeah, the board has way more functionality than I need, which is another motivating factor for finding something simpler and smaller. I have looked and looked, and the only thing I can find commercially that’s even close is a remote for a camera flash. Which is why I’ve gone down this road of figuring something out for myself. My electronics skill is limited and mostly self taught. I can do basic hacking of existing electronics pretty well (you should see some of the wack things I’ve done with a salvaged flash from a disposable camera), but this stuff is beyond my skill level, though I’m working to change that. I’m starting to get involved with the Maker community here in Minneapolis where I live, and have starting doing some active research and education (did you know that MIT has an electronics course available on iTunes University?).

Any tips on getting up to speed on this technology would be greatly appreciated. And if there’s interest I could post some pics and possibly some video of the blood rig in use.

5

If you are using a 9v and two AAs wired in series to get 12V then I’m pretty sure the 9V batteries are expiring long before the AA batteries do. A rechargeable 3S/1P LiPO battery with a capacity of about 2100mAH (see below) should last through the entire performance replacing the 3 sets you are currently using. You can get these from any R/C hobby shop (don’t forget to also get an appropriate charger) for $20-25. They are rated at a nominal 11.1-12.6V, are about 4.5in. long, weigh about 7oz. and should be good for 200-300 charge/discharge cycles before you need to replace them.

http://hobbyking.com/hobbyking/store/ca … -25(1).jpg

6

Some good news for you! ramsey electronics sells almost what you’re looking for over the internet, in a lot of places (amazon etc.).

It’s called a “Ramsey TXE433A RF Wireless Link Transmitter Module” and “Ramsey RXD433A RF Wireless Link Receiver Module” the module cost about $40 each. You would need to hook up the rx module to a power FET or 5 V coil relay(make sure that you put a diode across the coil , cathode towards the control signal) that in turn switches your +12 vdc. They are a LOT smaller than what you are using and can have 256 address for 256 unique receiver codes per transmitter. Great data sheets are at: http://www.ramseyelectronics.com/downlo … XD433A.pdf and http://www.ramseyelectronics.com/downlo … XE433A.pdf Apparently you use the “data valid” line which indicates that the 8 bit code received from the transmitter matches the 8 bit pattern on the receivers bit switch. The rx datasheet has good examples. Can you key the solenoid with a multimeter in series(set for current) and fresh batteries and see what kind of current it draws? How many minutes per show do you figure the solenoid is activated?

7

I’ve actually got a 6v solenoid valve that I want to use, to replace that 12v one.

8

the six volt probably draws twice as much current. You can’t cover a six ft. tall person with a 5 ft. blanket (not counting diagonals)

the ramsey module runs off of 7-12vdc (probably has an on board +5 v regulator). It really solves 95% of your needs in a very small package.

9

What kind of range do you need?

10

Also, have you tried the magic shop at 33rd and 7th? They outfit alot of decent stage acts and are very helpful. Even if they have nothing I need, I learn something every visit…

11

About 200’ usually does it. But I like to be on the safe side.

12

I too have worked on similar project it was based on Freescale MCU and RFM70 (RF Module) 8)

13

Linx Technologies has modules with ranges over 1000’. Check out their site. I would stay at 315 or 433 MHz in the area you are in for best range an lack of interference.

Ron