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Unfortunately I had to use surface-mount (SMT or SMD) devices for most of the components. While this is not hard with a bit of practice, it is perhaps takes a high-school electronics class skill-level. To make it as simple as possible, I have chosen the (physically) largest SMT components I could (1206), and have elongated the solder pads on the circuit board. However, two of the components (the 3K resistors on the backside of the board) are smaller than the rest (0805). This is necessary to provide enough clearance of the switch membrane that will cover over the resistors.
If you have never worked with surface mount technology, I recommend buying one of the several practice solder boards available. You can hone your soldering skills on those types of projects rather than risk damaging of your project. You will also want a capable soldering station. I use a Hakko FX-888D at the current time. Previously, I used a Weller WLC-100 which worked well enough. I also found a flat sanding stick that works well when removing those peskly little barbs on the circuit boards. The barbs are left over from separating the boards during the manufacturing process, and they can be annoying if not removed.
Receiver board. The receiver board used is fairly generic. Depending on your source, you may receive either reciver shown to the right. The receiver that the project was designed around (and the one you should receive when ordering from the Bill of Materials) is the left-most receiver, which I am calling Type A. However, there are some Type B style boards out there, and if you purchase one of those by mistake (or if they are all that is available), then I have designed an adapter board (RED lined part) listed in the Bill of Materials. You ONLY need to order the adapter board if you have receiver Type B.
The graphic to the right shows how the adapter board works in conjunction with the circuit board designed for RX Type A and using RX Type B. Generic header pins are used to make the connections. There should be ample clearance inside of the enclosure for the adapter board with the header's spacing. Also, if an external antenna is used, the antenna pin is different from the two boards as shown on the graphic. I am recommended attaching the Type B board to the adapter with wire rather than header pins. This board is slightly wider than the Type A board, and using wire rather than headers will let you offset the board slightly.
An alternative receiver mounting method that does not require an adapter board is simply use short jumper wires to mount the board as shown here. Since the pinout is reversed from the Type A to Type B boards, turning the board 180 deg will re-align the pin functions. If you use this mounting arrangement, I would recommend securing the receiver board with Silastic, Electronic-safe RTV, or other adhesive. Even if you did not use anything to adhere the board, it would probably remain secure. Unfortunately the main circuit board cannot be modified for header pins for the Type B board as they would interfere with the switch membrane.
Building the Circuit BoardThe thermostat requires an additional 12V power source. Since there is an ON-OFF switch on the thermostat for this power, there is no need to supply an additional ON-OFF switch for boondocking considerations. However, the 12V circuit should be fused at the distribution panel. There are two options for powering the circuit board:
The first option simply directly wires the terminal board on the thermostat to a 12V source. If this option is used, the terminal block shown in the green line of the Bill of Materials is required. The components in the yellow lines are not required. There is sufficient space on the backside of the thermostat to feed the 12V power source into the thermostat.
The second option powers the thermostat via the unused pins 1 and 6 of the RJ11 modular connector. This has a slight advantage in that you can easily disconnect the thermostat if needed (servicing, etc) without having to disconnect the hard-wired 12V source that would be required in Option 1. If this option is used, the yellow lines in the Bill of Materials are required. Even though the terminal block in the green line would not be required with this option, if it is included, the unit can alternately be bench powered (i.e. for servicing) with a 9V battery or other power source.
The instructions for building the power board (option 2 above) are also included in the PDF.
Modifying the EnclosureBefore we can install the circuit board, the enclosure must be modified. When the thermostat is disassembled, there should be 4 components; the front case, rear case, circuit board, and membrane. After disassembly, save the screws and mounting hardware for later. The stock circuit board is not needed and can be discarded (or kept if there is a desire to return the thermostat to pre-modified condition).
Modification A. From the backside of the front case, cut two of the ribs down as shown so that the circuit board fits flat. The circuit board has slots for the remaining ribs so they do not need to be cut. Modification B. Cut a slot in the case bottom as shown for the ON-OFF slide switch. Hint: do this after board assembly so you can trim to fit. Modification C. Drill a hole for the 3mm LED in the cover. Make the hole slightly small so the LED press-fits into the hole. You can also glue the LED in place from the backside using Silastic, 3M 5200, electronic grade RTV, etc.
Reassembly of the thermostat is pretty straightforward. Essentially, the circuit board is replaced, but everything else is re-assembled in reverse order of disassembly. Pay particular attention to how the power wiring is routed, which would be for Power Option 1. Note also that the LED simply routes from the circuit board to the backside of the front panel. A clearance notch in the circuit board adjacent to the LED pads has been provided for this purpose. Installation in the RV is similar to the previous removal step. However, if you are upgrading the thermostat version, you will likely have to drill new mounting holes in the wall in your RV. The footprint of the new thermostat should cover any holes left by the old style thermostat. And as indicated, you will have to find a way to run 12V power to the thermostat.
Receiver Programming
The typical 433Mhz receivers have their own termonology which may make it confusing at first to understand the modes:
I am also beginning to see a 4th mode in some of these devices - Delay. This is similar to Momentary mode but a specific time-lapse occurs before the output turns OFF. Typical delays are 5sec, 10sec, and 15sec, and they are often programmed as additional modes.
Before you can use the receiver, you need to set it up properly. Programming can be done after re-installation of the thermostat in the RV, or by connecting a 9V battery to the power terminals prior to re-installation (power is required to program the receiver, and it will run on 7~16VDC). Typically, these receivers come setup in the Latching mode, and Channel 1 on the receiver corresponds to Channel 1 on the Transmitter, and so on. There are three steps required anytime you need to re-program the recever. Note that in Steps 1 and 2, you depress and hold the receiver button Before you turn on power to the receiver. In Step 3, you depress the receiver button After turning on power. Also, Step 3 is a multiple pass process (pass 1 for RX Channel 1, pass 2 for RX Channel 2, etc).
Step 1 clears the current programming. This clears the Mode as well as all of the transmitter button mappings. Step 2 sets the receiver into Momentary mode. Step 3 assigns each transmitter button to a particular channel. You can assign any transmitter button to any receiver channel, as well as assigning all of the transmitter buttons to a single channel (you can assign about 50 transmitter buttons to any receiver channel, if you need support for multiple transmitters). Also realize that in Pass 2 thru 4, the receiver button will blink once, then twice, then three times, then four times - depending on how long you keep the button depressed. Simply release the receiver button After the LED blinks the appropriate number of times. There is also a timeout of a few seconds. After you release the receiver button, you have several seconds to depress the appropriate transmitter button. If no button is depressed, a timeout occurs and no button mapping will be set. If you make a mistake in mis-assigning transmitter buttons - say you assigned transmit button 3 to receiver channel 2 when you intended to assign it to receiver channel 3 - you must start completely over. That means, return to Step 1 and clear the programming, Step 2 and set the mode, then Step 3 and program each receiver channel. You can do Steps 2 and 3 in reverse order - i.e. perform Step 3 first, then Step 2. Also, you can do Step 3 multiple times. Say you map all of the buttons of a transmitter to the receiver, then later want to map a different transmitter... just perform Step 3 again.
Channel Mapping
There are a couple of idiosyncrasies when it comes to channel mapping - that is, assigning the channel on the wireless remote to the function on the receiver/thermostat. From a logic point of view, you might think Switch 1 on the wireless remote would be mapped to channel 1 on the receiver/thermostat, Switch 2 to Channel 2, and so on. However, when designing the circuit board, to keep the copper traces to a minimum, and transition from top to bottom (VIAs) at a minimum, it neccesitated connecting the switch channel of the receiver to a different switch number on the thermostat. The table below shows this relationship:
You will have to be mindful of this relationship when mapping the remote transmitter. For example, if you map (assign) Tx Channel 1 (on the remote) to Switch 1 (on the thermostat), Channel 2 to Switch 2, etc. you would end up with the functions on the wireless remote as shown in the left remote:
While this is OK, it might not provide the best intuition as to which button on which remote does what. In that event, mapping in the V3.2 order, the remote will be like the right one: So how do you do that? Simple. When you assign the transmitter buttons to the receiver, when the receiver LED indicates programming for Channel 1 (one blink of the LED), depressing Button 2 will assign the "OFF" function from the thermostat to the receiver/thermostat Channel 1. Likewise, when the LED indicates Receiver Channel 2 (i.e. blinks twice), it should be programmed to Channel 4, which is consistant with the table above. So in reality, you can program any button on the TX remote to any function simply by which order you assign the buttons. Keep in mind the mapping table for those assignments.
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