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Old Nov 25, 2004, 01:07 AM
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Downed Aircraft Beacon/Pinger - Minimum Parts/Cost/Experience

Downed Aircraft Locator Beacon/Pinger
NOTICE: Copyright 2004 John M. Albrecht - The information and images (data) in this post are provided free to the hobbyist community worldwide, provided that recognition is provided to the author and to “rcgroups.com”, and with the exception that these data may not be sold for profit. These data may be placed on other websites provided there is no fee or charge for access to the data.

Downed Aircraft Locator Beacon/Pinger - Albrecht 555 Type

I 've designed two types. This 555 integrated circuit timer based design requires absolutely the fewest possible programmerless components for a cheap, easy, and reliable delayed-action downed aircraft locator. My other design type uses the 556 dual timer chip, and is posted separately below at 24Nov04 23:12. In a beeping/flashing locator mode, using the 556 allows the LEDs to flash much more brightly, and the “pinger” beeps more loudly. However, it adds a few more parts and is a bit more sensitive to power supply voltage changes.

This is a design I came up with after reviewing what was available. I believe this design uses the absolute fewest parts possible for a reliable, non-constantly ON downed aircraft “Pinger” or “Beacon” that does not require a separate programmer (4 components for a “pinger”, 5 parts for a “beacon”, or 6 parts for a combination “pinger” /“beacon”). The app notes for the 555 chip showed how to make a simple time-delay circuit, and I proceeded from there.

I tried to produce a design that gives the user maximum choice with minimum work.

This design requires no interfacing with receiver signals. Such circuits are unnecessarily complicated and can suffer from false signals and operation.
In this circuit, you decide whether you want the pinger, the beacon(s), or both. You decide whether one or both the pinger and the beacon are set for constant or intermittent (beeping/flashing) alert.

It can be built in a couple hours using point-to-point on-chip wiring if you want.

I’ve provided several variations on the basic design, showing how you add or subtract the features you want.

Each diagram has NOT been optimized for a “clean” look. This is so you can more easily see the changes in each circuit…how parts move, are added, or are deleted to produce each effect.

Some observations and tips: Human senses are pretty good at seeing static images and hearing slight sounds. But, our senses are MUCH better at detecting things that are moving, and when lights and sounds are changing. It’s easier to find a beeping, blinking locator than one that is simply emitting a soft constant tone and a constant unchanging light…especially when we know what “signals” we’re looking for. The human eye is also generally most sensitive to green light. You may wish to consider using ultra-bright Green LEDs. You might want to use diffused vs. clear lens LEDs, as the diffused lens can be seen from a greater angle. If you use clear lens LEDs, you would have to use more of them to provide the same area of coverage. However, clear-lens LEDs do provide a more intense light when viewed from directly in front of the LED.

Description of Operation
Basically, from the moment you apply power to the circuit, “T” time (in minutes) will tick by. At the end of this time the pinger will start sounding, and the beacons will light-up. Power can come from the aircraft or from a separate battery…your choice…as long as the voltage is within the required values.

If your aircraft normally flies for 10 minutes, you can select R & C to delay for about 10 minutes. If it normally flies for 20 minutes, you can set to alarm after about 20 minutes. You control the delay. (Note: if you program the delay to start a few minutes before your flying-time usually runs-out, you’ll get a nifty doppler affected warning sound from your aircraft before the power runs out. If you crash early, you’ll have to wait for the timer to activate the locator.

The Piezo transducer and LEDs can be remotely mounted. You could even mount the LEDs at various points on the aircraft, so that it’s more likely you’ll see them from different angles. The LEDs can be any color, including White, although I had mixed results…you’ll have to try your “mix” and see if it works as desired.

The approximate time-to-alarm, T (in seconds) is determined by the formula:
Equation 1: T(seconds) ~ 1.2 x R(ohms) x C(uF).
For example, R=5megohms, C=100uF yields a Time of 1.2 x 5 x 100 ~ 600seconds ~ 10 minutes.

The brightness of each LED will be decreased the more LEDs you use. The volume of the alarm will be reduced somewhat if the intermittent beeping wiring option is selected. See alternate circuit examples for wiring options.
If you don’t want blinking LEDs, then you can replace the FLED (Flashing LED) with an appropriate resistor to limit the current to the LED(s). For Red LEDs in parallel, a value of about 100ohms (1/2W) is appropriate at Vcc=9V.

Something to consider in this case, is you’ll get brighter output by wiring the LEDs in series rather than parallel. See alternate circuit examples for wiring options. However, extra care must be taken to protect the electronics. This does, however, permit mixing LED types/colors for a more interesting beacon.
The number and type of LEDs you can add depends on VCC.

Circuit Highlights (BP-1, BP-2, BP-3)
IMPORTANT! All circuits were designed and tested with an approximate 9VDC power supply. Higher supply voltages will affect my discussions on LED current limiting and might affect operation. “Experiment” is the key word.

You can mix-and-match wiring options to obtain the features you want: beep/no-beep, flash/no-flash, loudest, brightest, etc.

FIGURE BP-1: is the simplest circuit, using the fewest components. It is an audio “pinger” circuit only. When Time Delay (T) is over, the transducer (Z1) will start a constant siren-like sound (note: you can buy piezo transducers that have beeping, warbling, or wailing sound-effects built-in, but many of them require more current than the 555 can deliver). You can add the optional flashing beacon LEDs as shown in the diagram. The more LEDs you add, the dimmer each one becomes. I’ve found 3 ultra-bright LEDs work well. Adding the flashing beacon option introduces a component called a flashing LED…commonly called a FLED. This FLED has a circuit built-in to the LED itself, which causes the FLED to “flash”. The rate and duration of the flash can be modified. The FLED can be used to control other devices. In my design, it can control the pinger and the beacon.

FIGURE BP-2: By changing the wiring slightly, you can change the transducer (Z1) from a constant siren sound to an intermittent beeping. However, the beep volume is lower than that of the siren in circuit BP-1.

FIGURE BP-3: This circuit wires the LEDs in series. This does two things: the LEDs can be extremely bright, and you have to be careful how many LEDs, what type of LEDs, and the selection of the current-limiting resistor (RL).

If you use too few LEDs for the RL you have selected, you can burn-out your LEDs or possibly the 555 chip.

However, with careful selection, you can run the LEDs with RL= 0 (in other words, you won’t need a current-limiting resistor, and your LEDs can be extremely bright). Use TABLE 4 as a guide in choosing LEDs and RL.
With RL=0, I found I could drive MY 3 Red Ultra-bright LEDs at a drive current of 20mA, or 2 Red LEDs with a drive current of 25mA, and nothing even gets warm. With 1 Red LED, the output current actually decreased, which I interpreted as a potential trouble indicator…possibly a 555 current limiting function…and did not pursue. I’d use a dropping resistor of at least 100ohms for 1 LED. However, in most instances the LED output seemed to vary by only a small amount whether I used the RL resistor or not…so, I’d use it to be safe.

I found that I could drive 2 White LEDs with RL=100 ohms and the output was blinding. This pushed 20mA. I also drove them with RL=0 for even more blinding output…but I chickened out after 10 minutes as I didn’t want to possibly burn-out 2 perfectly good White LEDs.

For the base design, the approximate values in TABLE 1 were tried and timed. You’ll probably want to test with your specific power supply and components. Timing accuracy is not real critical here. I successfully used the various LEDs shown in TABLE 2 in both parallel and serial configurations.
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Last edited by escudo; Nov 25, 2004 at 01:26 AM. Reason: format cleanup and 1 clarificatoin
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Old Nov 25, 2004, 01:12 AM
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Joined Nov 2004
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Downed Aircraft Locator - Design "556 Type"

Downed Aircraft Locator Beacon-Pinger - Albrecht 556 Type
This article is designed to be read in conjunction with “555 Type” article in my previous post. That design type is posted separately above at 24Nov04 23:07.

I've designed two types. This “556 Type” provides beeping/flashing locator mode, but allows the LEDs to flash much more brightly, and the “beeper” to beep more loudly than my “555 Type” design. However, it adds a few more parts and is a bit more sensitive to power supply voltage changes. This design is also more friendly to using a mix of LED colors…just calculate the right RP value for the +Vcc and LEDs you are using.

FIGURE BP-4 shows a circuit that flashes VERY bright LEDs, and beeps a fairly loud piezo transducer. (remember, that in my simpler 555/FLED circuits that beeped the transducer, the volume was reduced because of the voltage drop through the FLED. This is not the case in circuit BP-4.

The app notes for the 555 chip showed how to make a simple time-delay circuit and astable multivibrator, and I proceeded from there.

I tried to produce a design that produced a useful circuit with the minimum parts.

This design requires no interfacing with the receiver signals. Such circuits are unnecessarily complicated and can suffer from false signals and operation.

You can delete either the flashing beacon (D2-n, and RP) or the beeping “pinger” (Z1) from the output section, and the LEDs and/or “pinger” can be located at strategic points on your aircraft, away from the IC, or the IC can be glued “dead-bug” style to Z1.

It can be built in a couple hours using point-to-point on-chip wiring.

Some observations and tips: Human senses are pretty good at seeing static images and hearing slight sounds. But, our senses are MUCH better at detecting things that are moving, and when lights and sounds are changing. It’s easier to find a beeping, blinking locator than one that is simply emitting a soft constant tone and a constant unchanging light…especially when we know what “signals” we’re looking for. The human eye is also generally most sensitive to green light. You may wish to consider using ultra-bright Green LEDs. You might want to use diffused vs. clear lens LEDs, as the diffused lens can be seen from a greater angle. If you use clear lens LEDs, you would have to use more of them to provide the same area of coverage. However, clear-lens LEDs do provide a more intense light when viewed from directly in front of the LED.

Description of Operation (BP-4)
Basically, from the moment you apply power to the circuit, “T” time (in minutes) will tick by. At the end of this time the pinger will start sounding, and the beacons will light-up. Power can come from the aircraft or from a separate battery…your choice…as long as the voltage is within the required values.

If your aircraft normally flies for 10 minutes, you can select RD & CD to delay for about 10 minutes. If it normally flies for 20 minutes, you can set to alarm after about 20 minutes. You control the delay. (Note: if you program the delay to start a few minutes before your flying-time usually runs-out, you’ll get a nifty doppler affected warning sound from your aircraft before the power runs out. If you crash early, you’ll have to wait for the timer to activate the locator.

The Piezo transducer and LEDs can be remotely mounted. You could even mount the LEDs at various points on the aircraft, so that it’s more likely you’ll see them from different angles. The LEDs can be any color, including White. Try your “mix” and see if it works as desired.

The approximate time-to-alarm, T (in seconds) is determined by the formula found in Equation 1A. For example, RD=5megohms, CD=100uF yields a Time of 1.2 x 5 x 100 ~ 600seconds ~ 10 minutes.


Circuit Highlights (BP-4)
FIGURE-BP4: This circuit is provided only for those that want to have an easy, cheap, very bright, very loud timed locator that both beeps and flashes. You’re limited only by Vcc2 and the current handling ability of the transistor Q1 you use.

This requires 3 sections of control: (1) the delay timer, (2) the oscillator that provides the beeping/flashing control signal, and (3) the power driver for the pinger and the lights.

The delay timer and the oscillator are combined in a LM256 Dual Timer chip. The power driver is just a general purpose NPN transistor suitable for the currents and voltages you want to control.

When connected to Vcc, the circuit draws about 8mA until the Time Delay has expired. Once it’s timed-out, the current dominated by the current drawn by the transducer and your LEDs. This will probably be in the neighborhood of 30-50mA, depending on your circuit choices.

Determining the value of the various resistor and capacitors in this circuit can generally follow these guidelines (for 9VDC supply):

Time Delay Circuit
Equation 1A: Value of RD and CD for seconds of delay before locator starts.
RD, CD: T(seconds) ~ 1.2 x RD x CD (Delay ~ 12 minutes for RD=5megohms, CD =120uF )

Beeping/Flashing Frequency Circuit
Ro,Co: See TABLE 8
(556 chip astable operation timing is easier to just provide some basic values. You can experiment to get what you want out of it. However, values too far from those I used will probably not work)

Flashing Beacon Intensity Circuit (See TABLE 6)
Equation 2: Value of RP for a given Vcc2 and number and type of output LEDs.

You can tie Vcc2 to Vcc1 for simplicity, or a separate higher value for more LEDs)
RP= E/I = (Vcc2 - Vtransistor - (sum(VLED))) / Imax.

Here’s a practical example. Let’s say your maximum current for one of the LEDs is 20mA (you always choose the lowest “maximum mA” allowed). You have 4 Red LEDs. The voltage drop across the transistor will be about 0.7volts. Using the LED Voltage Drop values from TABLE 7, we see that VLED(red) ~ 1.9 volts. Thus, sum(VLED) = 4 x 1.9 volts ~ 7.6volts.

Therefore,
RP = (9.0 - 0.7 - 7.6) / 0.02 ~ 35ohms. (33 works just fine)
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Last edited by escudo; Nov 25, 2004 at 01:20 AM. Reason: provide companion 555 type post timestamp
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Old Nov 25, 2004, 02:00 AM
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Joined Nov 2004
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This is pretty good stuff. I'm reasonably certain it will all function as described. But energy management is everything with this type of device. 555s are workhorses, but even from a component count standpoint Micros are hard to beat.

Please don't take this the wrong way, the real advantage of your info is there is no programming to deal with, and every stinking one of the parts will be available local to most folks. I'll probably head to the bench and junkbox to build all of these this weekend, just because.

Great post and GREAT EXPLAINATIONS!!

Cham
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Old Nov 25, 2004, 06:11 AM
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Joined Nov 2004
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Thanks for the feedback. No "taking the wrong way" here. You covered most of what I hoped to achieve: cheap and easy (available/junk-box parts, no programmer needed, few parts). I've been micro-controller programming for years, but still like to play with the simplist stuff, help people see how things work, and encourage experimentation.

I didn't try it, but one could probably use a CMOS timer chip and achieve effectively 0 power-drain until timeout. These kinds of circuits can also be easily implemented using CMOS inverter or NAND gate chip and they can work over a voltage range of 3-15volts.
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