Newbie Question......Suitable power supply

[Gorhad]

Hi guys

Firstly I have no knowledge whatsoever of Electronics and RF, my background back in the UK was electrical but I specialized in the manufacture design and installation of Electric Heat Trace Systems for tanks pipe lines etc

I recently purchased

http://www.ebay.com/itm/2KM-Long-Range-RF-link-kits-w-encoder-and-d...

For a project imp trying to develop

Basically I have a fluid level float switch with 3 independent reed switches that when the fluid rises/falls to the 3 individual points they draw together and form a circuit

Example

Float 1 High level

Float 2 Ideal Level

Float 3 Low Level

The float switch itself will be mounted some 50 feet from the main equipment (pump and control panel)

Hard wiring between those 2 locations would be completely impractical, so I have gone down the thought pattern of RF wireless control

The float switch would sit in a bulkhead with a small weatherproof box on the top containing the transmitter and transmitter power supply and around 50 feet away in another weatherproof box would be the receiver with its own power supply

With the help of a fantastic new friend in Chennai (India) I have managed to get to the stage where the connections for the 3 reed switches to the transmitter are ok and the pairing between the transmitter and receiver also.

But honestly I don’t want to keep pestering him, even though he doesn’t mind.

My question is regarding the best power supply to the transmitter (remember no hard wiring)

So I'm assuming a battery supply contained within the weatherproof enclosure and I believe I need 5 volts?

Then secondly would be the power supply for the receiver (this can be powered by a hard wired device as its in an area where it would be practical

I'm sorry to be a pain and burden you people but your help would be greatly appreciated

 

[davenn]

for the remote transmitter, ( 3V - 9V) you could look at a rechargeable battery ... something easy to recharge
like a sealed lead-acid, and a solar panel charger for that battery

Yeah you could use lithium or nickel metal hydride but they have more complex charging restrictions
so lets keep it easy with a sealed lead acid type
looks for something like a 12V panel with around a 10W-20W output. and a charger controller to drop that
12V down to ~ 7 to 8V for the battery.

there's a starting point for you

Dave

 

[Gorhad]

Thanks Dave...Ebay a good place? and what terminology should i use

Many thanks

 

[hevans1944]

... so I have gone down the thought pattern of RF wireless control. ...

Apparently you did not go down the thought pattern far enough.

The device you purchased is not authorized for unlicensed use in the United States. The 433 MHz ISM band is restricted to Region 1, which includes Africa, Europe, and Russia. The USA, the Americas, Greenland and some eastern Pacific islands are in Region 2, where this band is reserved for radionavigation and licensed amateur radio (70 cm band) use only. This is enforced by the Federal Communications Commission (FCC) with authority to levy heavy fines, imposed on a daily basis, and to seize unauthorized equipment. It is likely that your use of this equipment could interfere with radio amateur activities in the 70 cm band, and if so, they will report you to the FCC in a heartbeat. I know I would. Hams are very protective of the few frequency allocations available for amateur radio communications.

A much better (and legal) bet would be one of the "Wi-Fi" bands, with an appropriate narrow-band line-of-sight antenna on both ends of the communications link. Look into operation on 915 MHz, 2.450 GHz and 5.800 GHz, which are popular wireless LAN router frequencies.

73 de AC8NS
Hop

 

[Gorhad]

Thanks Hop ......just glad i didnt complete it YET...many thanks

 

[Gorhad]

So could you point me in the right direction please

 

[hevans1944]

I figured with your background experience being in Great Britain you would be unaware of the issue. The 433 MHz stuff is quite legal and popular on the other side of the pond. I don't think the Chinese (Region 3), who make most of the cheap stuff, give a fig who buys it or where it is used. Google is your friend here. Start with this search string: 2.45 GHz GSM telemetry. I think what you are looking for will be a long-range Bluetooth solution.

 

[hevans1944]

So could you point me in the right direction please

Are you looking to build something, or are you trying to find a commercial off-the-shelf solution? I am working with Arduino Uno modules and XBee (Bluetooth) shields. These can be setup for peer-to-peer short-range communication, but they do require some electronics and programming expertise. Give us a hint what your budget and time frame for completion is. What you are trying to do is quite common. You just need the right frequency band and appropriate hardware and software.

 

[Gorhad]

Yes I'm trying to build something for myself initially, which was prompted by one of by customers


I have a pool care service and one of my customers an elderly lady has a real hard time emptying her pool after a heavy rain because she suffers with arthritis


Also she recently went on vacation to Europe for a month and came back to a huge water bill.


Memorial day her pool filter ruptured and because the equipment continued running drained 3/4 of the water from the pool before the neighbor noticed and turned the equipment off


Hence the attached drawing (PDF) and explanation

 

[Gorhad]

Originally I was going to hard wire between the float switch and control device but it would be cosmetically and probably physically impractical

 

[hevans1944]

Have you selected the float switches yet? How are you planning to install the switches in the pool (you mentioned mounting them to a bulkhead... what's that)? What length of cable will connect the float switches to the transmitter? Will you perhaps mount the switches in an open-ended PVC pipe with wires coming out the top? If the transmitter end is to be battery-operated, how will you provide access to the electronics, the battery, and perhaps a solar panel to re-charge or maintain charge on the battery? Have you considered fail-safe operation in case there is a failure of the communications link?

Depending on the amount of power needed, you could possibly incorporate the transmitter, battery, and a small solar panel into a water-proof box that is attached to the float switch tube and secured to the lip of the pool in a sunny location at one end of the pool. I think you mentioned this in your first post.

I presume you have a prototype of the float switches, and have tried them out with a hardwired connection, perhaps with the details worked out with your friend in India. All you need now is the wireless connection, right?

What does arthritis have to do with pool maintenance? Are the diverter valves normally manually-operated, instead of motor-driven, and therefore require some hand strength to operate in most pool installations? Just curious.

 

[Gorhad]

Thanks for your input hevans1944

I've attached a few PDF of drawings i have done that might give you a better idea of it

The float switch is a multi level unit that will mount directly into the pool skimmer lid itself. It will also have what they call a slosh guard around it to prevent the turbulent water (bathers) from causing false switching

On top of the skimmer lid will sit a small weatherproof box IP65 or maybe 67 which will encompass the float switch tip with the wires protruding out and also contain the transmitter etc

The valves normally are manually operated and are 3 port for even me they take some force to turn, so for an elderly lady with arthritis you can imagine

Example she called me yesterday evening nearly in tears because we had just had a heavy thunderstorm and the pool was quite high , asking if there was any way I could get there in the morning and drain it down a little

I just want to help her and maybe others in that situation

Also attached are the drawings (wiring and partnering of the transmitter and kit I purchased on eBay), which unfortunately as you said is not authorized for unlicensed use in the United States

So that’s where I'm totally at a stand still

 

[hevans1944]

Well, since you have all the parts, why not wire everything up and see if it works? If it causes interference and someone complains and you get a notice from the FCC, then you can go to Plan B. Just don't start cranking out a bunch of these as a "favor" until you get the legal ramifications nailed down! It is my understanding that "Part 15" of the FCC Rules and Regulations governs unlicensed transmitters. You are apparently free to build as many as five hobby transmitters for use on just about any frequency that does not cause harmful interference to licensed users of that frequency. But if you want to sell such things, the transmitters need to be approved by the FCC... an expensive process. This is why many manufacturers buy "type approved" RF modules and incorporate the modules in their end product.

When I was a teenager, I built a small transmitter that produced a signal in the AM broadcast band. I used it to "broadcast" music from a record player to radios in my neighborhood, all the time living in mortal fear that the FCC was going to come knocking on my door at any time. It never happened, perhaps (1) because operation was intermittent a few hours in a day and (2) output power was miniscule. My friends and I used portable radios to try to determine what the range of my signal was. Turned out that it was not detectable on those portable radios from about a block away. That brought a sigh of relief until I realized the FCC might have much better and more sensitive receivers than I and my friends had been using. So I lost interest in the whole idea of hosting a pirate broadcasting station during the evenings after school and moved on to other things electronic.

 

[Gorhad]

hevans1944

Are there kits on the market like the one i brought off ebay but use a different frequency that i can legally use?

 

[Gorhad]

How about a security gate and garage door opener like this one

http://www.ebay.com/itm/850LM-LiftM...-Door-Opener-Universal-Receiver-/190962226268

 

[hevans1944]

@Gorhad I have been reading the Code of Federal Regulations (CFR) Title 47, Subpart 15, which governs the use of unlicensed low-power transmitters in bands that are otherwise licensed. Apparantly the original 70cm band transmitter you purchased is legal to use in the United States provided its RF power output is less than 200 μV/m at a distance of 3 m and it is type approved by the FCC. Presumably it would not be allowed for import if type approval had not been granted, but your mileage may vary. You should look for an FCC type approval sticker pasted to the transmitter signifying type approval. Or you can "build" up to five prototypes for your own (not commercial) use without needing type approval.

So, even though it is operating in an amateur radio band, as long as it doesn't cause any interference with licensed users in that band it will be okay to use it.

Just about any frequency of operation from DC to Light is available for use under Part 15 regulations, with certain bands of frequencies being "off limits" because of the potential to interfere with public safety communications. That includes 322 to 335.4 MHz and 399.9 to 410 MHz among many others. I have attached a little PDF from Texas Instruments (who make transmitters) that pretty much outlines the Part 15 requirements in language ordinary folks can understand.

The garage door opener would work, but it seems to be way overkill for your swimming pool valve application. I would go with what you bought originally. Please accept my apology for the diversion. Looks like I was mistaken in my opinion.

Hop

 

[Gorhad]

Hop you are awesome

Would you help me find a battery power supply for the transmitter side please? I was hoping to get something small to fit inside the waterproof box with the transmitter and float switch termials in

 

[hevans1944]

Since your float switches will change state (open to closed or closed to open) very seldom, it is unnecessary to have the transmitter energized all the time. Even a 2.5 mA load, applied continuously, will drain a battery eventually unless the charge is replenished by some other power source, such as line power or solar power. What you need to do is add a circuit that monitors the switch states, and when the state on any switch changes energize the transmitter to send the new state to your receiver. If you do that, a standard 9V "transistor radio" battery will last for months or even years:

Since you will visit the pool on a regular basis for pool maintenance, it would be a simple matter to replace the battery as needed. Maybe even replace it whether it needs to be replaced or not... these batteries are dirt cheap.

I wouldn't want to get too fancy with this, but there are many ways to monitor the three switches, determine when a switch changes state, and then operate a small relay or a transistor power-switch to briefly energize the transmitter. You have spare signal inputs on the transmitter, so your circuit could also monitor the battery terminal voltage and send an alert signal to the receiver indicating the need to replace the battery. The best way to do that would be to periodically measure the terminal voltage under a "dummy" load and send the alert (energize the transmitter) only if the voltage was less than a selected "trip point" value.

There are many small μPs available for this task, one being the PIC from Microchip. These can be put to "sleep" by an internal program so they awaken on a change of switch input. While asleep, they draw less than ten microamperes of current. At that current level, the life-time of the battery is essentially the same as its "shelf life" which is several years. The internal program is written to and saved in Flash memory (like the kind used in USB memory sticks) that is an integral part of the μP, so it is non-volatile. You program it once and you're done.

Are you up for building a couple small circuit boards, one for the transmitter and one for the receiver? I know you said you were an electronics newbie, but this type of project should be well within your capabilities. And it's a lot of fun! Plenty of people here at Electronics Point will help you.

Hop

 

[Gorhad]

Absolutely Hop

Im quite determined to see this thru its interesting and a challenge for me. Brings back memories of wjhen i was designing electrical control panels and systems for Heat trace applications. Ive been out of that field for 18 years and oh boy whether its a mid life crisis or not im eager

 

[hevans1944]

Yeah, I can appreciate your feelings. It was years since I programmed a microprocessor when I ran across this thread here at EP. The idea of using a μP that cost less than a buck really caught my eye, so I ordered up a bunch of them (along with a PICkit 3 Programmer) and had at it. Man, what a steep learning curve that was! I am still climbing it. My first mistake was believing I could jump right in with an SOT-23 sized chip, which is about the size of mustard seed, barely visible to the naked eye. My second mistake was not reading and understanding all of the information on the datasheet for the chip I was using... a PIC10F206. There are certain "features" enabled by default that have to be disabled in your program before other things, like bi-directional I/O ports, will work. Figuring that out delayed my climb up the "learning curve" by several months! I even thought my chips had been damaged by something I did while "wiring them up" to DIP headers for use on a breadboard. See below for a picture of a typical breadboard.

The software (MPLAB X IDE) to develop programs is free from the Microchip web site, and parts are readily available from Digi-Key and other distributors. You can also buy parts in a "kit" usually aimed at Arduino hobbyists. Things like little push-button switches, LEDs, capacitors, resistors, reed relays, and similar items. Last year I purchased a beginners electronic kit at Radio Shack in Virginia Beach to give to a grandson as a Christmas present. When I got back to Dayton I went to a local Radio Shack and purchased one for myself, just in case he had some questions I could answer on the 'phone. You should consider purchasing a similar kit to learn electronics at home. Mine cost about sixty dollars and required several (six IIRC) D-size dry cells to power it up. It included two booklets describing how to wire up several hundred circuits, enough to keep a small boy busy for maybe three or four months. The main thing I liked about it was it included a breadboard pre-connected to the dry cells and several permanently mounted components on the front panel you could connect with jumper wires to components you mounted on the breadboard.

You can (and should) purchase a bulk assortment of 1/4 watt resistors, either on-line or at your local Radio Shack, along with a variety of capacitors, diodes, potentiometers and the like if you don't purchase a learning kit with those parts already in it. For that kind of stuff it does pay to shop on-line and use Asian parts. I would avoid Asian sources (no matter how cheap!) for most semiconductors because you never know what you are going to get. There are a lot of counterfeit parts out there, passed off as genuine. Those parts may or may not work, and you have little recourse if they don't work. Caveat emptor. Most of this stuff is very cheap compared to the shipping costs.

So, with all that in mind, you need some basic things to begin this journey. The first thing is a little device called a solderless breadboard:

These can come with binding posts or not, mounted to a panel with non-skid feet or not, and full-size (like the one shown) or half-size. Most electronics learning kits will have one as part of the kit. The two rows of holes at the top and bottom, arranged in five groups of five holes, are all connected together in each row to form four "bus bars" that you connect power to. Sometimes the two sections of five on the left and right are not connected together, giving you eight bus bars if you need that many. All the rest of holes are connected vertically in groups of five holes on either side of the center space. You components are connected to these holes with jumper wires between components. Plastic Dual-Inline Package (PDIP) integrated circuits with pins spaced 0.1 inches apart straddle the center space.

You will also need LOTS of jumper wires in a variety of colors to connect everything together. These can be 24 AWG insulated solid conductors, or stranded conductors (for flexibility) with pins soldered or crimped to the ends. You need several hundred of them in assorted lengths and colors.

I am currently finishing up the programming for a PIC10F206 that will control a small flashlight. The PIC "sleeps" most of the time, waking up only if there is a button press or a timeout from a watchdog timer. While it is asleep it draws about six microamperes from a one microfarad "energy storage" capacitor, the voltage supplied to the PIC dropping from about 5 V to about 4 V while it is asleep. A few microseconds after it wakes up, it re-charges the capacitor for one millisecond through a 330 Ω resistor, does some "housekeeping" chores and then goes back to sleep. It sleeps most of the time, so the average current is way less than ten microamperes. Except for the one millisecond "wake-up call" every 135 milliseconds or so (more often if the button is pressed rapidly), the μP is sleeping, drawing almost no current.

Hop