Tech Forum

The two solutions above are good but I think they are both overly complex. I assume that the reason for the time delay is that the wireless system produces a pulse whose duration is too short to properly trigger (and latch) the garage door relay. I know that my garage door will stop if the button push is of too short a duration. So we need to stretch the signal from the wireless system and we probably need to make the voltage of the wireless system compatible with the 24V relay in the garage door opener.

Looking back a couple months in Nuts & Volts there is an article about a circuit that turns on a laser to help park a car at the proper place in a garage. The circuit uses the sound of the garage door opener's operation to turn on the lasers for a minute or so. The article is Nuts and Volts - May 2012 - Page 40 - "Build a sound-activated laser parking system." I think the second op-amp stage from that circuit might be all that you need.

The op-amp is setup as a comparator with the reference voltage level set by Potentiometer P1. The other input is from an amplifier stage but I think you could just directly couple the wireless device to that op-amp input (perhaps via a largish value resistor to give some isolation). You would set P1 so that the reference voltage is a bit less than whatever the wireless system puts out.

When the wireless signal is high the comparator swings to the voltage rail charging cap C2. When the wireless signal goes away the op-amp goes off but C2 is kept from discharging back through the op-amp by diode D1. The voltage on the cap turns on the mosfet T1 which you can use to control the current to the relay's coil (replace the laser diodes with the relay's coil in the circuit). The combination of R5 and C2 controls how long the mosfet is turned on.

In the publication the author was going for a couple minutes. If you only want a couple seconds then R5 and C2 can both be made smaller to decrease the on time. As a rough estimate the on time is about 2/(R5*C2) seconds. So R5=1M and C5=1uF should give an on time of about 2 seconds.

I assume that the need is to have a delay before opening or closing the garage door. The circuit diagram below will do this.
 

The circuit shown here, uses a 1Hz oscillator (ICL555) which clocks a 4015 shift register as a sequencer. When the output of pin 2 goes high, the 4N35 optocoupler conducts. The output shorts across a garage door pushbutton.
 

The "Desa Int’l wireless doorbell" will need to close the switch shown as "Enable PB." This can be done with either another optocoupler or suitable transistor logic to simulate the switch closure. In operation, the Enable signal (pin 15) must be active high long enough to be captured on the next clock edge. When the yellow LED goes on, the input has been captured. For the circuit shown, the delay is about four seconds. Increase the clock frequency by decreasing the 560K and/or 330K resistors in the clock section.
 

Note the series wiring of the RLED resistor, optocoupler (LED), and red LED. The 47 ohm resistor must be changed if the circuit is to operate on higher voltages, up to the 15 volt limit of CMOS. Use Ohm's Law to get 20 mA of current through the optocoupler / RLED combo. For the RLED value shown (47 ohm), a six volt supply is required. In practice, I took the circuit board from a cell phone car adapter and "floated" it with a diode to get the six volt regulated output. From a 24 volt source, I use a 12 volt series zener to drop the voltage to 12 volts to the cell phone car adapter. A one watt zener is sufficient.
 

Originally, I tried using a CD4060 for this, but found the circuit to be more predictable. The approximate component placement is shown below the circuit. Actual wiring may vary! The circuit has been in operation for over six months now and works great. If an actual pushbutton is used, the circuit may have potential electrostatic discharge susceptibility through the pushbutton to the D input. While I have not had issues with this, I have a small grounded loop near the pushbutton to reduce static discharge through it. Using a pushbutton with a grounded static shield is recommended.
 

Most parts (including the solderable breadboard) are from AllElectonics.com, though the 4015 is from Digi-Key.

This sounds like a classic application for the ubiquitous 555 timer IC.

The datasheet for the 555 includes many examples of using it, including the one-shot circuit that I think will meet your needs nicely. You can use a common transistor like the 2N2222 to drive the relay coil. Don't forget to put a reversed diode across the relay coil to protect the transistor.

Hi, Gary! I am a ham (amateur radio operator) and here is what I know about Yagi antennas (actually Yagi-Udi antennas, but that's a story for a different time).

I would advise against WD40, as it will almost certainly mess up the impedance where it matters (at the driven element). But first, a bit about Yagis.

A yagi antenna is constructed such that the center point of all the elements (other than the driven element) is grounded to the mast. So shorting the elements to the mast is done at the factory for all but the driven element.

The driven element is the one that connects (usually via some sort of matching network) to the coax, and my bet is that THAT is where you need to focus your attention.

Also, there are affects on the antenna from 'nearby' objects, including 'ground' (or anything horizontal below (or even above) the line of sight of the antenna). If the 'nearby' objects are enough wavelengths away from the antenna and not in the 'line of sight' then their impact should be minimal.

However, 'ground effects' can be helpful or hurtful, even out to multiple wavelengths away from the antenna. This is where 'higher is better' comes from. By the way, the higher the antenna is above 'ground' the better the antenna works.  However, if you mount an antenna higher above the earth, but your rooftop is in the line of sight to your other antenna, your 'ground level' is the roof, not the ground you walk on! (Especially at the frequencies we are talking about here).  So, all other things being equal, it is better to put the antenna on the side of the house closest to the antenna you are 'talking to'.

For more information, I recommend the ARRL Antenna Book.

Anyway, back to the question:
There are a few places where you are likely to lose signal strength:

1 - At the end of the coax, or inside the end of the coax. If water gets into the coax, it will change the characteristics of the coax such that you WILL lose (lots of) signal strength. If the coax terminates in a connector of some kind, then you want to protect the connector from water. If the coax does not terminate in a connector, then does it end such that the wire angles DOWN to the end of the coax or up? If up, then you have a great place for water to get in to the coax. If possible, orient the coax such that water on the coax will not travel toward the open end of the coax. In either case, protect the end of the coax, and all connections, with something non-'conductive' at RF (at microwave, to be more precise). Either some sort of silicone sealer, or use a plastic margarine tub or similar (assuming the antenna is far enough from the chimney to avoid melting the plastic!). Before using a sealant, make sure it is not conductive at microwaves (PVC is notorious for being conductive there). If in doubt, one partial test is to place some of the material, along with a cup of water, in a microwave and cook for a while (start with a few seconds, if the material in question does not get hot, go for longer). If the material will 'bother' your antenna then it will likely get hot (or at least warm) in the microwave. Do this same experiment with your margarine tub also!

2 - At the matching circuit. What sort of matching circuit is being used will determine how easily affected it will be by water and  so forth, but generally the matching circuit wants to be dry. Some stay drier by design than others. In any case, the margarine tub from 1 could probably be placed over the entire driven element and coax end. Another possibility would be to build a 'roof' for the antenna, but if you use metal or anything affected by microwaves (see experiment in 1 above), then you need to keep it a reasonable number of wavelengths away from the antenna.  Since we are talking microwaves, or at least 900MHz, then that isn't so bad as trying to build a roof for an HF antenna! If I remember correctly, 5 to 10 wavelengths away should be more than adequate. At this point, I should recommend the ARRL antenna book, as it has MUCH more info, including the frequency to wavelength formula and how far you should put the 'roof.' You might get away with 1 to 2 wavelengths away, IF the 'roof' is not resonant at the frequencies of your internet provider. This is where the ARRL Antenna Book is probably your best bet.

3 - At any point between the antenna and the receiver where water can enter the coax.

Since you say that the fireplace seems to exacerbate the issue, then you probably have a combination of soot/whatever plus water in the matching circuit, coax, or both.

Random ideas and thoughts:
Can you move the antenna further from the chimney?

Perhaps you need to shield the antenna from the smoke as well as from the rain.

Rather than moving the antenna higher, is there anywhere else where you still have line of sight to the cell tower (or whatever is the other end of your radio circuit)? In other words, if you could protect the water-sensitive areas of the antenna, AND move it to where it does not pick up 'stuff' from the chimney that would be a win-win. One concern is  water dissolving stuff from the fire that then attacks and corrodes the antenna!

Given that we are working with at least 900MHz, as long as you have line of sight to the other antenna, anywhere on your roof should be almost as good as anywhere else. In fact, if you have a clearer shot 6 feet lower, then 6 feet lower is better, as long as you don't move your roof, (or neighbors roof), into the 'ground effect' area) So, if you can mount the antenna away from the fireplace and still get a good signal, that's probably better all the way around. In fact, as I say, start out with the side of the house closest to the other antenna.

Bottom line: weatherproof the coax, especially the ends; protect the matching circuit from excessive water; keep the exhaust from the chimney from mixing with water and depositing on the antenna (possibly by moving the antenna elsewhere).

Water combined chemicals in smoke from a fireplace could get into connectors and cause signal loss in Gary Rathburn's antenna system. He notes, "If it's rainy and we're not using our fireplace for a few days, the signal also improves."  Perhaps the rainwater by itself flushes some soluble chemicals out of the connectors. It's unlikely water on the antenna or rain droplets cause a problem.

During a dry period, wrap exposed connectors with Coax-Seal or Scotch-brand "2228 Moisture Sealing Electrical Tape." Better yet, replace the connectors and the cable and then seal the new connectors. If moisture and chemicals from smoke got into a connector, they probably got into the cable too. Also, always create a drip loop to keep water from running down cables and into connectors.

If you try to "seal" the antenna, you can de-tune it and cause signal loss. Antennas are manufactured to work outdoors in bad weather.

Yes, fire makes carbon smoke a conductive. I'd try a plastic bag to see if it corrects it. Or, place a shield one foot under the antenna.

I suggest you try wrapping the elements of your Yagi antenna with PVC electrical tape. It might protect the antenna enough to provide the necessary improvement. As a young "shop gopher" in a two-way radio shop, I earned many hours of minimum wage wrapping two-way base station antennas with electrical tape. The owner of the shop insisted it reduced received noise and extended the life of the antenna.

It sounds like you have a faulty cable and/or cable connector at the antenna. I would replace the cable with Wilson 400 low-loss cable, and put a boot on the connection at the antenna to keep out moisture.

Additionally, the Wilson 301111 Yagi is quite directional; try aiming.

If it has been several years since you installed the antenna, maybe more cell towers have been built in your area.

I think you should look at the connectors. They may not be water tight!

Electrical duct butter, electrical duct seal, and coax seal can all be used to encapsulate the connector and socket area to seal it from water inclusion.

I’ve used Beam antennas up in the air for decades with good results.

The first place I saw the oscilloscope multipath display was on the Marantz 10b. Two other FM tuners with the scope outputs were the Scott 312 (and the Scott 312b, plus the kit versions LT112 and LT-112b) and the Heathkit AJ-15 (and the receiver version AR-15). You need an X-Y oscilloscope — preferably with response down to DC. Connect the horizontal X input to the output from the audio detector (still monophonic, not yet demultiplexed) and connect the vertical Y input to the AGC (automatic gain control) signal.

Check out the Oersted Technology article at http://oersted.com/magnetizing.PDF.

I'm reading between the lines here,  so I apologize up front if I'm in the wrong universe with my answer.

I see 2 main approaches (off the top of my head) - build an LED illumination thingy from scratch, or buy LED spotlight bulbs 'off the shelf' and fabricate whatever you need to get enough light.

Get It Off The Shelf
A fairly long search on google found all sorts of possibilities, if you only want to get some E26 base bulbs and create an array of <n> LED spotlight bulbs to supply he desired light level. If you assume your 200W incandescent bulb puts out something in the neighborhood of 3000 lumens, then you need about 7 or 8 420-lumen spots like the Grainger 3CRA2 (Optiled model 1503050217) - which Grainger sells for $45 each… Or just 3 of the 6XWKD (GE Lighting LED20P38S830/25) which puts out 1050 lumens (at $60 each) would also supply the desired light output.

If you want to go this way, google is probably your best friend. (Along with eBay). Use "LED spotlight" or "LED high-power" or "LED 20W" (or even "LED e26", which is what I started with).

Build It Yourself
Googling for 20W LEDs, I found www.hero-ledstore.com/heroled-20w-led-c-2_184.html with all the parts you'd need to make a 20W LED lamp (but that's gonna run you about $74 and you still need 2 of them (apparently they are 1600 lumens each). Interestingly, the parts to make a 50W (4000 lumen) 'system' are only about $175 - and you'd only need one of those… There are other options out there also, I'm sure, as a google for "high power LED" returned about 78 million hits "wink." The thing there is that you need a constant-current source to feed the LEDs with, not a constant voltage (but with voltage limits, IIRC).

Look here www.pjrc.com/teensy/td_libs_DogLcd.html

Of course, you can use two three-way AC switches or double pole switches. It is easily available in market. If you have the knowledge of electric powers than you can also do easily yourself, otherwise call electrician. You can get here https://aashirwadinterior.com/services/industrial-electrical-contractors-vadodara-ahmedabad/

The problem with standard SPST switches connected in parallel, if either is left on, the other cannot turn off the fan. If the switches are connected in series, when one switch is left off, the other cannot turn on the fan. The solution is a three way switch arrangement.

This uses two SPDT switches instead of the SPST version. Either switch can turn on or off the exaust fan. If you are not familiar with 3-way switch wiring, go to your home repair store and get a book like "Home Wiring For Beginners".

There is one problem, if someone turns on the fan in the first room, someone in the second room can turn it off if they did not notice the fan was running.

The answer to question # 2124 "Two AC Switches, One Fan" by Stan Strom on page 80 of the March 2012 edition of Nuts and Volts will not meet the questioners needs.

The circuit shown in the figure is a neat implementation of an inverted eXclusive OR (XOR) circuit using switches. In this circuit the fan relay will activate (thus turning the fan ON) when BOTH switches are in the ON position or BOTH switches are in the OFF position (XOR output is high if either input is high BUT not both inputs high). With the switches in opposite positions (ON-OFF states) the relay will deactivate and turn the fan OFF. [I have had students try to use switches to simulate logic gates like this. Good job Stan!]

Looking at 120 VAC bathroom fan specs, most draw 0.8 to 1.5 amps. If you have a light fixture with two (2) 60-watt bulbs, they will draw 1 amp. The 14-gage (14 AWG) wire used in most lighting circuits will handle 15 amps at 120 VAC and most lighting circuits are on 15 amp breakers. [Be sure to check that the bathroom lighting circuit is capable of handling the extra fan load just in case the installer was cutting corners]

Most vent fans are powered from a 120 VAC switch without a relay. I would locate the light fixture junction box and simply hook one 14 AWG wire from the HOT side of the lamp (its the BLACK wire if the light was wired in standard fashion, if the fan does not run when the switch id ON use the other wire at the light fixture) in each bathroom to the hot terminal of the fan. The vent fan neutral is hooked to the lighting circuit neutral. This hookup avoids using two (2) extra switches and a relay. One of the tenets of reliability says: "The more parts in a circuit, the more probable the system will fail." A tenet of economics says: "The more parts in a circuit, the more the circuit will cost."

If you want separate switches for the fans and lights, just wire the fan switches like the light switches but run the HOT wires from the fan switches to the HOT terminal of the vent fan. Two switches in parallel turned ON at the same time will not hurt anything, they will each carry half of the fan motor's current.

The original question mentioned using logic gates. The logic circuit would be simple: Hook the HOT wires from the light switch to the OR gate inputs through a device that converts 120 VAC to logic level voltage (e.g, an opto-isolator) and hook the OR gate output to the vent fan  HOT terminal through a relay (logic voltage rated coil and 120 VAC rated Normally Open contacts). This circuit would have a reduced reliability and higher cost due to the high parts count. Engineers try to minimize parts count whenever possible.

On the mechanical side, be sure to vent the bathroom fan's exhaust to the outside to avoid mold and mildew in the attic. Also check all electrical and building codes to make sure you do not anger the "regulatory gods."

Sorry for the wordiness but engineers try to cover all of the possibilities.

All that is necessary to make two switches control a single relay for your bathroom fans are two single pole double throw switches. They're very often sold as three-way switches for controlling a lamp with two switches and are readily available at Lowes or Home Depot.

Feed the hot line (the black mains wire) to the common terminal of one of the switches; the two legs of the switches connect to one another — these are called 'traveler' lines. The relay connects between the common of the second switch and the neutral line (white mains wire).

Using the circuit below, if the relay is energized, then flipping either switch will turn it off. Then with the relay off, flipping either switch will turn it on. It is shown in the on position.

Maybe I'm missing your intent, but it seems you should be able to just wire two 120 VAC switches in parallel.  Either OR both switches on will turn on the fan.  Both switches off will turn off the fan.

I can see no reason not to connect two switches to one fan, that is, in parallel, as long as you check that the same circuit provides the "hot" lead to each switch. The US standard is Up = On, so it would be relatively easy to see which switch was used to turn on the fan.

If you are rewiring anyway, I would use single pole double throw switches as they are used when controlling a light with two or more switches. Then flipping any one of the switches will change the mode off to on or on to off. This requires that some of the cables have a third conductor known as a traveler.

If I understand this, then all you need are 2 three-way wall switches. One at each location of the two vents and then either switch will control the fan.

A simple solution is to use a three-way switch at each of the two locations (connected with a 3 wire cable) to control the Fan. Most wall switches are “single pole, single throw”. Outwardly, three-way wall switches” look the same, however they are single pole, double throw. Analogous to your situation, a common three-way switch use is to have one at the top & one at the bottom of a stair connected to control a light on the stairway.

Three-way wall switches” are inexpensive, easily found at home centers, electrical and hardware stores. The wiring is not complicated and there are many Internet sites for details, e.g., www.electrical-online.com/electrical/diagrams/

We have three bathrooms and one exhaust fan which is ducted to all three rooms. Our solution was to use a double pole switch in each room (commonly available in regular toggle wall switch format) where one pole does the lights in that room, and the other pole is wired in parallel with the second pole of the other two switches, and then to the fan motor, so that if any of the three switches is turned on, the fan runs, as well as the light in only that room turns on. Be sure to take safety all precautions, and follow electrical codes, as we are dealing with 110 VAC.

Use two three-way AC switches. These are very commonly used for lights so two switches can control the light. It will allow switching the fan off from either location no matter which location turned it on.

The problem might be getting the wire from switch #1 to switch #2 but since they both control the same fan there should be a way to get the needed wire from one to the other.

The switch instructions that should come along with them, or a good "How To" book will show how to wire them up correctly.

Although it doesn't use a microcontroller, Intersil described a circuit for making an auto-ranging DVM in their Application Note AN046. The URL for the PDF file of this article is www.intersil.com/data/an/an046.pdf.

Their basic circuit (Figure 1 in the app note) is for a 7106 DVM chip which is meant to drive an LCD display and run off batteries. A modification of that circuit is required to use a 7107 chip which uses a dual supply instead of a single supply, and has a higher power drain due to the LED display needs. That modification is given at the end of the Intersil article, in the text and in Figure 8. This circuit design utilizes the over-range/under-range states of the DVM chip to trigger the auto-ranging function, so depending on your application it might be of benefit to use an improved DVM chip that incorporates a zero-integrate phase feature to improve the recovery from over-range. Some manufacturers have added zero-integrate phase to their modern versions of the 7107 (e.g., Maxim), but DVM chip versions that explicitly include this improvement include the 7136 chip (sub for the 7106) and the 7137 chip (sub for the 7107). I noticed a couple of minor typos in the Figure 1 circuit of this article. The CD4028 logic chip is mislabeled as CD402T, and both output lines are labeled as over-range ("OR") instead of one line being labeled over-range ("OR") and one being labeled under-range ("UR").

After a bunch of looking, I found this on Amazon. www.amazon.com/DROK-Synchronous-Voltage-Converter-Waterproof/dp/B00J229O9A/ref=sr_1_36?ie=UTF8&qid=1418062090&sr=8-36&keywords=dc+dc+converter+Buck

You didn't say how much power you needed but, this looks pretty robust. Good Luck