|Anatomy of the GE
Remote Plus Receiver
and Conversion to General Purpose
Relay Control Output
Model RF100RXPS or 51140
Several years ago I purchased a GE Whole-Home Lighting Control Kit to allow controlling the lights around my home while away. For more details on this system and my conversion to a internet (Ethernet) based control see my article GE Smart Remote Ethernet Interface.
The picture above is of the original GE Plus Receiver Indoor Outlet Adapter model RF100RXPS. This adapter allows the direct 120VAC control of any appliance, light, radio or whatever you want via the RF link to your home controller unit. Anything up to 1200 watts resistive load can be sourced directly from this units AC output connector. A recent project to modify one of these adapters to provide a remote reset for a vintage SYM-1 computer had me ripping one open to trace the schematic and make the required changes and additions to facilitate my new use. In this document I address a slightly different modification, which is much easier, to simply change the output to a general purpose normally open (N.O.) relay output. Thus the reader could use this remotely accessible relay to control other items around their home that require a switching of lower voltages or even higher DC voltages perhaps.
Here's what I needed to do:
1) Determine how to open this darn unit.
2) Trace out the circuit and explain how it works.
3) Describe the changes to convert this to a generic N.O. Relay remote control box that will still work as original as one channel in the GE Smart Home system.
Opening the Adapter Cabinet
Opening the cabinet wasn't as easy as I would have expected. In fact I'm not sure how to do it without damaging the case a little. The enclosure is held together via the top and bottom ends and in-order for me to get it opened I needed to cut into those areas with my Dremel tool and a cut-off blade. Here is a picture of the enclosure opened up:
If a reader determines a way to open this enclosure without damaging it please let me know and I will provide those instructions here. For now you will probably need some glue to get things back together once you have made the required modifications. There are three circuit boards inside the unit. The large board contains the GE remote receiver module and all the control circuitry. The little board on the lower left contains a surface mount LED that lights when this adapter is turned on via the GE controller unit. The other small board above the LED board is the channel selector switch board. GE went all out to make the channel selector switches in their adapters about as cheap as possible. On the many units I own it is this selector switch which is often the cause of adapter failure, with the output relay coming in second. What happens is the little shorting contact assembly that is rotated via that front knob often falls off and no longer makes contact. In that case the adapter still works but you will discover it only works on Channel 1. As you will see later, when I describe the circuit, if their is no contact being made in this selector switch it will be interpreted as channel 1 by the internal decoder.
Let's have a closer look at the main circuit board.
The AC input, the connector that plugs into the wall outlet, is located on the right side under the circuit board. The AC plug prongs solder directly onto the circuit board. As you can see the Green (Ground) and White (Neutral) wires connect directly to the AC output outlet that is on the left hand side of the picture. It becomes obvious that this adapter switches only the Black (HOT) wire in our AC line. It goes from the AC input plug to the lower left side of the circuit board next to the small blue cube. That blue cube is the control relay that connects our HOT lead to the output outlet when this adapter is activated by our GE controller unit. The other black lead on the left side of the relay can be traced to the output relay.
GE Smart Remote Plus Receiver Circuit
Below is the schematic diagram of the GE RF100RXPS outlet adapter. Please note you can click on the schematic (and other pictures on this web page) to bring up a larger view. In addition you can view a pdf version of the schematic by clicking here. All part identifiers are those that are silkscreened on the printed circuit board.
The adapter is not a complicated unit. Let's start at the upper left. That is where the AC arrives from our home outlet. As you can see the Ground (GND) and Neutral (NEU) lines run directly to the output AC outlet that is located on the devices bottom when it is plugged in for use. The neutral is also connected to ground in our circuit through a small inductance of what is known as a ferrite bead. A ferrite bead is a passive electric component used to suppress high frequency noise so it can not enter, or leave, our adapters circuitry. As far as our 60Hz AC voltage entering the adapter the ferrite bead looks like a direct connection and does not affect it at all. Our HOT AC line connects over to one of the poles (contacts) of our control relay RL1. This HOT lead will also supply the operating voltage for our adapter. The two resistors R1 and R2 along with the capacitor C1 make up a voltage divider circuit to drop down our 120VAC line voltage to an acceptable level to operate our adapter. The negative half of this lower AC voltage is chopped off by the diode D2 (sent to ground) and the positive half is rectified by the diode D1. The electrolytic capacitor E1 and capacitor C2 filter our pulsating DC into a smooth ripple-free DC voltage that is around 24VDC which is used to activate the control relay RL1 as I will describe later. The 24VDC is connected to resistor R3 which drops it to approximately 5VDC to supply our Remote Control Decoder IC (PT2272-L4) and our receiver module RX1. GE was very good about providing additional distributed capacitors, C3,E2 and C4, throughout the circuit board to keep any voltage ripple and transients from being propagated on our control circuits power source.
The Receiver module (RX1) is located at the top of the adapter main board as shown previously. Communication from the GE Smart Home controller unit is transmitted via a 320MHz RF link (UHF) at only around 3MW power. The receive adapters, like this one, all contain little receivers tuned to that same 320MHz frequency and they demodulate the digital coding that is superimposed on that RF signal. That spring device that is attached to the RX1 module is a helical wound antenna. The demodulated data is supplied to the remote control decoder IC PT2272-L4 via pin 14 (DIN). The PT2272 is produced by Princeton Technology Corp. in Taiwan. If you review my other article on the GE Smart Home controller unit you will read that it uses a matching encoder IC PT2260. Our decoder IC will respond to any ON or OFF commands being sent by the controller unit if we are set to the same Home and Channel settings encoded into our received data string. As you can see the PT2272 has address lines that provide the input to our decoder as to the selected Home and Channel we have this adapter set to. The Home setting is via a two small switches that are located on the back side of the adapter (wall side) and are accessed through a small removable cover. The channel selection is done via that front panel switch labled 1 to 8. As I mentioned previously this channel selection switch is a weak point on these adapters and often are the cause of failure. A knowledgeable person could repair the switch in most cases, but if yours works don't detach that switch circuit board from the front cover piece. The switch is set up to provide a binary coding to the address lines A0 through A2 on our unit. It's actually a complimented logic binary. Here is a table that shows the logic levels on those address pins for the different channels.
The switch (SW) will ground the pins that are represented as a 0 in the table above. If this switch contact assembly fails, often it falls off behind the plastic switch knob, all the pins will remain ungrounded and thus we will always be selecting channel 1 no matter where the front knob points.
So now if our received and decoded signal from the home controller unit agrees with the Home and Channel selection applied to our PT2272 IC it will respond to any ON or OFF command. When an ON is received it will set the output data pin D0 (pin 13) to a high logic level or approximately 5VDC. When it receives a OFF signal it will set that same pin to a low logic level or below 0.8VDC. The D0 output is a latched output and remains in its ON or OFF state until changed by our GE Home controller or if the adapter loses power. When it is set ON the 5VDC will drive the transistor Q1 to an on state. That will allow current to flow from the collector to emitter of the transistor and complete the circuit for the relay RL1's coil. Thus the relay will close its contacts and the HOT AC lead from our home outlet will be connected to the HOT lead of our adapters AC output outlet. Our connected AC device will turn on! Also, notice the front adapter LED is also part of this Q1 current path and it too will light to indicate the adapter is in the ON state. Once an OFF command is received by the adapter the D0 output goes low and our transistor Q1 turns off. Thus we no longer have a closed current path for the relay and LED and as a result the relay opens and the LED goes off. We no longer have the HOT lead connected to the adapters outlet and our connected device will turn off.
That's the operation in a nut-shell.
Converting your Adapter for Relay Output Control
Maybe you will not always want to control a 120VAC device, but instead something that runs off a battery or low voltage DC source. We could easily modify this circuit to do just that. We could still use the same AC outlet but instead wire the adapter up to provide the original NEU and HOT connections as simply the output of our relay contacts. The black wire going to the output outlet is already wired correctly. We just need to remove the white neutral wire that connects from that output. That's easy to do with a simple snip (or unsolder) of the white wire that runs from the input (right side of earlier picture) and unsolder it from the output outlet. That white wire gets fully removed. Next we will take the black wire that runs from the relay (left side of blue relay box) and unsolder the end that is connected to our input (right side of earlier picture). Now attach that black wire to the output outlet connection that originally had the white wire connected to it. When all is completed we will have both black wires that connect to the circuit board next to the blue relay connected to both the HOT and NEU terminals of our output outlet. Now when our unit is turned on via our GE Home Remote controller these two terminals will be shorted together to complete any external circuit path.
It might seem strange to use an AC outlet to act as a connection for the relay closure and I would agree. But this describes a cheap and easy method to achieve this end. I will have another page on this site that describes my conversion of this adapter to provide a TTL logic level reset control for my SYM-1 computer. In that case I completely repackaged the original adapter, even to the point that it no longer even really needs an AC power source. If properly modified we would no longer need the relay and thus the only circuitry would all operate off of 5VDC and could feasibly work off battery power to supply the RX1 receiver module and the PT2272 decoder IC.
The GE Smart Home controller is a fun and cheap unit that opens up a whole world of remote control around the house. I hope others will find these series of articles useful/
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