Tights with a heartbeat-EDN

2021-12-14 14:15:53 By : Ms. Lisa Shao

Wait, wait, what? The heartbeat straight jacket is a standard canvas straight jacket with some fancy electronic equipment to create a sweet garment with remote wireless function. To get the full effect, a person puts a special stethoscope on their heart, and they will see their heartbeat on the tights I wear. This tutorial is about my 2007 Halloween costume.

Okay, why? I want to create a project around EL (Electroluminescence) wires-sometimes called cold neon lights. It is this neat, very flexible, and very bright wire that shines well in low-light situations (such as Halloween!). With a little work, you can control the EL and get some interesting displays. Most importantly, I need a piece of warm clothing, because the weather in Boulder at the end of October will become very ugly (usually sleet). The tights are the perfect platform for electronics, warm, and strange enough for Halloween (and Burning Man).

Stethoscope: I want to create a simple way to interact with the jacket. I could use a heart rate belt or some other way to get the user’s heartbeat, but I want to use a stethoscope because I think it’s more friendly than having someone wear a heart rate belt. I think I can use the microphone to "hear" the heartbeat, and then transmit the heartbeat to the jacket.

What have I learned? I learned that this project is more like a sociological experiment! Many people are quite timid about putting a stethoscope on their bare skin (no, they work without clothes). Maybe it's the fear of sterile, cold metal touching their skin-the doctor's office coming back to bother them. Maybe they are afraid of contracting the deadly viral skin chewing horse disease (stupid). I'm not sure. Another interesting thing I learned is that people rarely find their hearts (oh no! I'm dead!).

Something i have to find

Learn how to use EL wire

The first thing I had to do was to allow my ATmega168 microcontroller to control a single channel. In other words, a string of EL wires is turned on and off. The EL line is a bit tight in terms of control. The EL wire needs 125V AC at 425Hz. This is a fairly high voltage and a strange frequency, but the current is very small. I may be able to design a circuit to generate this, or I can buy an inverter. Note: The 125V/425Hz output from the inverter is enough to sting your fingers. There is not enough shock to really worry about, but enough to draw your attention to the exposed communication connections.

Connect the AC inverter to the EL wire and it really lights up. Now I want to control. How to turn on and off the AC power connected to the EL wire? With triac! These are beautiful "switches" that allow you to turn the AC power on/off. perfect. Take out the Digikey Bible and try to find a good one. I chose MAC97A4GOS-ND parts. The inexpensive TO92 through-hole is easy to weld and can handle currents up to 0.6A at 200V. Wow. I hope we don't do such a big thing.

This is the DC current reading I found into the inverter:

I found that you can run my inverter without load, no problem. The results may vary. So you can see that the stranded wire of the EL wire uses about 25mA (DC) depending on the length. Comparable to LED power consumption.

The next step is to make the wireless work between the tights and the stethoscope. I choose nRF2401A because I like Northern Europe. These low-power, low-cost ICs are perfect for simple "Hey! Heartbeat type signals. The signal the stethoscope will broadcast is low data rate (I need about 4 bytes) and low bandwidth (4 bytes* per minute) About 70 times). In retrospect, I should use nRF24L01. It is easier to use and has better specifications than nRF2401A, but both can be used.

Initially, I used two radios in the same breadboard so that I could send and receive firmware. In the end, I boiled all this down to a few well-functioning nRF libraries. If in doubt, please use RTFM from Nordic IC.

Now using all this knowledge learned from the breadboard of TRIAC and the radio, I have created two PCBs, the EL controller and the stethoscope transmitter.

The circuit board shown in the picture is not filled with RF or TRIAC. The EL sequencer receives RF triggers and controls the EL string, up to 6 independent channels.

In this case, each channel is a concentric-shaped EL wire. Admittedly, this PCB layout is really bad. Since I laid out it on 10-2-07, we have learned a lot. The main goal is to show you how to use a microcontroller to control EL through TRIAC. To do this, check the schematic.

Here you can see that we send high voltage (HV) alternating current through the connector of the connection line. When the EL_E pin goes high (3.3V), this will turn on the TRIAC, allowing AC to flow in and out of the EL wire, making it light up. Make sure to include a current limiting resistor in the TRIAC! 1k works well.

The auscultation RF board that enters the stethoscope must be as small as possible. It is powered by a small lithium polymer battery, except that it reads the analog level on the microphone to try to capture the heartbeat and play "Hey! Send a heartbeat signal to the tights."

Now do some testing! The first step is to let the EL sequencer control a string in the jacket. This is a string connected to the sequencer, inverter power supply, AC output, and end of the LiPo.

The next step is to create a series of five hearts. This involves some work. If you have never used an EL wire, here is the step-by-step process of soldering to this evil phosphorous beast.

Before you delve into the EL wire project, please consider how the EL wire will be connected to your controller. I highly recommend the JST 2-pin friction connector:

This type of JST connection will allow you to quickly remove the wiring harness or remove the controller from your clothes. Step 1: Cut and peel off the outer sheath

You can't even see the wire in this picture, but the EL wire has a phosphorous center core (the thick white wire in the picture above) and a hair-like wire circling around the core. If you strip the wires too rough, you can easily cut (or tear) the wires like hair. This requires practice. I suggest picking up an EL stripper. These slippers are helpful, but still require practice.

Step 2: Scrape off some phosphor

Use an x-acto knife to scrape the phosphor from the core. In the image above, you can see two hair-like spirals.

For my own sanity, I connected all the cores with red wires and all the hairs with black wires. Remember to put the heat shrink tube on the red and black wires before soldering! I use tape to fix everything while soldering. Works well.

Now carefully solder the hair-like wires. You can see my hair wrapped around the black solid core wire. I use x-acto blades to help hold the hair in place.

After welding, shortly before heat shrinkage.

Note that a single wire is heat-shrinkable. This helps provide some support for the hair and also isolates the core connection from the hair connection. In order to shrink heat shrink, I like to use a cheap heat gun. In a pinch, I have used matches or lighters.

Adding a heat-shrinkable final overall jacket will significantly increase the elasticity of the connection. These connections may seem fragile at first, but in the past few years, I have beaten these connections. One connection failed-this was the first connection I made, and it was very bad. With a little practice, you will create an excellent and reliable ELwire connection.

Okay, repeat now. There are 4 more times. what. This is the most painful step in the project. very slow. But once it is done, I have a heart!

I programmed the jacket so that if it does not receive a heartbeat, it can enter the demo mode, and the heartbeat turns on and off at different speeds.

This is the inside of the jacket with LiPo battery, AC inverter, EL Sequencer, and various lines leading to the EL wire.  

In order to form the EL wire and connect it to the tights, I used a convenient button device. The device uses neat plastic "staples" to reattach buttons to clothing. It is also very suitable for connecting EL wires to clothes!

The next stage of the project is to connect the stethoscope. I want the oscilloscope to look as "off the shelf" as possible.

I bought a cheap stethoscope online and started to crack it.

The next step is to solder the wires to this little guy. Not trivial, but not too difficult. Be sure to prepare two microphones to prevent the pads from being lifted during the soldering process. Please pay attention to the tape that secures the microphone when I use it. I used 30AWG wire so that I can easily pass the wire through the flexible tube of the stethoscope.

If you pull hard enough, the head of the stethoscope will fall off the tube. The diaphragm cover of this cheap version can also be unscrewed. I use small heat shrink tubing to keep the wires together.

Next, I roughly cut a small slit in the rubber tube, and the electronic device will be connected to the tube. I used the thicker 22AWG wire again so that I could fish along the tube, connect the microphone cable to this thicker wire, and then pull it all back.

Reassembled the head to the tube, and I connected the microphone cable to the RF auscultation board.

I used a hacked microphone board to amplify the audio signal. Hot glue secures the fragile 30AWG wire in place. Then feed the amplified signal to the ADC on the ATmega168. I had to partially expose the electronic device so that I could charge the battery and open and close the circuit board.

In practice, the microphone input can hardly pick up the heartbeat sound. It works, but it is not clean. When it works, I find the effect is really amazing! However, in public, most people find the flashing tights more interesting than the "function" of a stethoscope.

'This is a fun Halloween costume!

To see more creepy projects and stories, please read this Halloween special.

"English, buddy. By the way, this is a tights. Strait = narrow, bounded... Straight = no curve."

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