LED Distance Indicator Dog Harness

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Introduction: LED Distance Indicator Dog Harness

About: Electrical Engineering Instructor at University of Santiago de Chile.

I usually take my dog Rusio for a walk when the sun goes down so he can play without getting too hot. The problem is that when he's off the leash sometimes he gets too excited and runs further than he should and with the low light and the other dogs it's not easy to spot him right away.

To solve this I had the idea of making a dog harness that will glow red when he goes to far from me, as an added requirement I wanted to make it without using any microcontroller or programming to make it as accessible as posible for other makers.

****Disclaimer****

This project keeps a walkie talkie constantly "talking", this actually jams the frequency band that it's using in the near range of the emitter which might be illegal in your country (and even if its not illegal it's not a nice thing to do). This was overlooked during the design and will be addressed in a future version.

Supplies

  • cheapest pair of walkie talkies you can find
  • 2x 555 ICs
  • 1x 2n2222A transistor
  • 2x TIP120 transistor
  • 7x 1Kohm 1/4W resistor
  • 1x 5.6Kohm 1/4W resistor
  • 1x 6.5 ohm 1/4W resistor
  • 2x 220ohm 1/2W resistor
  • 1x 470nF 10V capacitor
  • 1x 10nF 10V capacitor
  • 3x general use diodes (I used 1n4004)
  • LEDs of your color preference

Step 1: Walkie Talkie Disassembly

The plan is to use the communication range of a cheap walkie talkie as a makeshift distance indicator, for this the first part is disassembling it and checking how it works!

Most cheap walkie talkies use the speaker as a mic too, the function changes when pressing the button to talk and we are going to use this for our advantage. One walkie talkie will be continuously "talking" and the other one "listening", if the listening end can't hear the talking one it means that they are to far away and we can use that as a indication to turn the lights on.

Step 2: "Talking" Walkie Talkie

To achieve a continuously talking transmitter first we need to keep the "talk" button pressed, for this the button contacts can be soldered together.

The need to be talking all the time will get tiresome really fast so instead we are going to use a signal generator hooked to where our mic/speaker is supposed to go. The generator will be a 555 astable circuit powered from the battery pack of the walkie talkie (6V on my case), the circuit can be seen in the image and the component values selected should generate something close to a 1KHz square wave on the output.

It's important to check which end of the speaker goes to the negative of the battery pack as this will be soldered to the ground of the generator, the other end is connected to the wire labeled as "out". Also the output of the 555 is clipped with a diode to have a voltage in a range similar to the voltages generated when talking to the mic.

Finally we add a LED to know when it's on and we close the walkie talkie with all the new circuits inside.

*The falstad txt export is provided if you want to tinker with the component values.

Step 3: "Listening" Walkie Talkie

Then we proceed to disassemble the second walkie talkie, this time the talk button is not pressed and the wires that goes to the speaker will be used as our input to check if the lights should be turn on.

The first part of the circuit is a half wave rectifier that charges a capacitor when a signal is present (we are close enough to hear the transmitter) and a parallel resistor to discharge the capacitor when the input signal is not present (too far from the transmitter). Also a resistor of similar value to the speaker is placed in its place to trick the original circuitry into working as intended.

The output voltage of the rectifier is used as input for a schmitt trigger (comparator with different on and off thresholds) made with a 555 IC, we use a diode as voltage reference giving a ON voltage threshold near 0.45V and a OFF on voltage threshold of around 0.23V. The output of the schmitt trigger drives the TIP120 that powers on the red LEDs when our circuit can't hear the other walkie talkie.

As an optional feature I added a logic inverter (by using the 2n2222a) to drive a second TIP120 that will turn on green lights when the dog is in range of the "speaking" walkie talkie.

Finally everything was soldered with the exception of the LEDs and put into a box (original walkie talkie was too small), the connection ends for the LEDs were left accesible for connection later and a power on LED indicator was added as a final touch.

*Falstad txt import is attached as well, the changes in the input takes about a second in real life to switch between lights but in the simulation it takes forever because of the simulation step size.

Step 4: Harness and LEDs

The final step is to put the LEDs on the harness (I made my own test harness from a couple of belts bolted together), I went with 3 parallel groups of 2 series LEDs for both red and green leds. The total voltage of the supply should be greater than the forward drop of the series LEDs plus the drop in the transistor that is about 1.5V for the TIP120. In our case we have:

red: (2.2V)*2 + 1.5V = 5.9V < 6.0V

green: (2.0V)*2 + 1.5V = 5.5V < 6.0V

With the calculations done we go forward and poke some small holes for the legs of each LED and they are put in place and soldered on the other side with small wires (I salvaged some from an old ethernet cable). Afterwards some padding is added to protect the dog from any pointy bit of the LEDs legs or solder joints. Finally both ends of each LED group are soldered to the terminals that were previously prepared on the "Listening" walkie talkie.

Step 5: Test Walk

With all the previous steps we are ready for a test walk! I went to the park with Rusio at dusk as usually. The whole setup worked as intended with a change to red lights when he goes 6 to 8 meters away from me, after that he need to get closer to return to the green lights.

As a final suggestion for the people trying this instructable it seems to be a better idea to just go with the red LEDs as the green ones serve no actual purpose by being on when the dog is near. I added them mainly to show clearly the two states that can be detected, but the problem is that they dry out the battery pack quickly as they are almost always on.

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    11 Comments

    0
    hmv4u
    hmv4u

    1 year ago

    i was wondering if you could do this but in reverse,instead of the dog harness coming on when it gets to far away how about a long range remote control and a 12v receiver for the harness which you trigger when Rusio gets to far away-puts on the leds & if you wanted to get fancy you could even put in a voice command chip - " Rusio, come back you little **** " ;0)

    0
    coffeeguy123
    coffeeguy123

    1 year ago

    This is a VERY cool idea! One important issue, though, is you're using walkie-talkies which, when used for this purpose, violate Part 15 and possibly part 47 of the FCC rules; the reason being that you're using part of the radio frequency spectrum set aside for walkie-talkie use and basically 'jamming' whatever channel that the walkie-talkies are running on, so for this application to be legal you'd need to change the frequency used by the transmitter and receiver. There are several modules out there suitable for this purpose. Again, not bashing you or this idea; it's very creative and easy to construct. Is it likely that you'll be creating harmful interference? Probably not, but it's still illegal. Incorporate something such as this (see link below) with the appropriate power levels and you'll be all set!
    https://www.jameco.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10001&productId=2297703&catalogId=10001&langId=-1&CID=GOOG&gclid=EAIaIQobChMI4cL62dv55wIVAuDICh0_IQjPEAQYASABEgI_RPD_BwE

    0
    Azze01
    Azze01

    Reply 1 year ago

    Even with the legal contemplation set aside, it's not a nice move to block an entire channel, so you may want to update to a less "invasive" version (same for me: No bashing meant)
    Other than that, I really like the idea behind the invention and its simplicity. Keep going on!

    0
    javier.borquez
    javier.borquez

    Reply 1 year ago

    You're right, I never stopped to think about the federal regulations (Here in Latin America such things are rarely enforced) but I should have considered it.
    For a version 2 I'll definitively try the suggested Transmitter Receiver Pair, with the compatible encoder/decoder that is used with this pair I could even remove the problem when multiple RF links are in range! (as pointed out by mrbonine)

    0
    coffeeguy123
    coffeeguy123

    Reply 1 year ago

    Ah...I missed the fact that you're in Chile. I'm an amateur radio operator in the USA (near Atlanta, Georgia) and was listening to several contacts in Chile and Ecuador last night on the 80-meter band. My Spanish isn't very good but at times I was tempted to transmit in Spanish...also prohibited here in the USA unfortunately. I'm going to be using this idea for a couple of applications, and am thinking of using an RC circuit with the 555, then using a missing pulse detector on the receiver side to see if it helps extend the battery life. Of course, that makes the circuit a little more complicated...Me gusta como mantenistes su diseno mas sencillo, con componentes disponibles en todos paises!

    0
    RaymondR6
    RaymondR6

    1 year ago

    This is niece as a pure analog solution, and very simple to understand and build. I am lucky that my own dog (a 12 year old Llasa Apso) doesn't stray far from me when I walk, so I don't need this project. But I recommend it for those dog owners who tend to lose their pets. I recommend adding an audio output at the collar (transmitter) and train the dog to search and walk back to the owner when the audio signal is active.

    0
    javier.borquez
    javier.borquez

    Reply 1 year ago

    That's a great idea! I could even use the original speaker of the walkie talkie!

    0
    mrbonine
    mrbonine

    Question 1 year ago on Step 5

    Wow! I've had this exact problem and settled on a super white reflective collar only used in these circumstances (rare because risk to Bart getting into street or river or game is too high) plus a very powerful LED flashlight with blinding output combined with training so he would know that light = me. But enough low tech, 2 practical concerns: sensitivity changes as battery discharges (and knowing the status) leading to distance changes: what is the real distance limit and can, should it be adjustable? Even circuit age will affect this. Other concern, interference. Given one park & two humans with dogs chance if this on same freq + proximity are low, but RF noise, squelching, etc, how effective and reliable? I don't want to be ominous but life/death could be impacted. But is your invention better than my collar & flashlight? Hell yes!

    0
    javier.borquez
    javier.borquez

    Answer 1 year ago

    After testing it for several days the emmiter battery is still going strong but the receiver battery has to be changed frequently and when it starts to dry out the range is reduced to about 4mt before not being able to turn the red LEDs anymore.

    And the interference should be possible, anyone broadcasting in that same frequency will trigger the receiver to think that it is near to the user.

    If i ever put together a version 2 i'll see how to address this issues.

    0
    mikecl4d
    mikecl4d

    1 year ago on Step 2

    This is awesome. You are a true value to the community!