How To Make a Hearing Assist

[TKSnake[TK]]

Sometimes it's hard to hear in a bucket, especially if one has loud blower fans running. There are two main options people will use: use quieter fans (sometimes not an option in hot places) or use a hearing assist.

 

Hearing assists can be tricky to install, but if you're handy with a soldering iron, they're actually not too hard to build using an off-the-shelf kit, extra wiring, and a shrink wrap. I did this work years ago for myself, but for those interested in learning how to become a maker, I'll include some additional thoughts here.

 

My original build blog for the hearing assist

 

Part 1: How to Solder

 

I covered this in an older forum post that you can find here.

 

Part 2: The Velleman MK136 Super Stereo Ear

 

 

IMPO it's the worst-kept secret that this off-the-shelf kit is the heart of most hearing assists used in TK buckets to date, because it's prefab and inexpensive. When you're paying for a hearing assist that's put together, you're mostly paying for the person's time to put it together, which isn't trivial.

 

That being said, with some time, effort, and slight modification, you can install the kit with the included microphones into your helmet, and wire them back to the main board for amplification to the headphones or ear buds of your choice.

 

The kit is still widely available on Amazon and other online retailers. You can use this link to search Google.

 

The kit is easy to assembly because the instructions are clear and all components are through-soldered. This means there's no surface-mount soldering, chips, ICs, etc. to solder. It's 100% analogue. Just put the leads through the board, solder them, and trim the excess lead with wire clippers.

 

There are plenty of video tutorials discussing how to put these together (try these YouTube videos).

 

However, before you add the microphones or battery pack, pay attention to Part 3.

 

Part 3 - Modifying the Velleman to Use in your Helmet

 

The Microphones

 

 For the default kit, the mics are soldered directly to the board, where you don't want them. They need to be mounted close to the outside of your helmet without being seen.

 

To do this, you'll want to solder about 12" / 30 cm of lead wire between the microphones and board, maybe more depending on where you want to mount the board inside your helmet. An easy way to measure is to use wire or string to measure between where you plan to mount the board and where you plan to mount the microphone. If in doubt, give yourself extra wire. It's not hard to add more wire if need be, but it's extra work that can make an extra point of failure.

 

There are two main things to remember when mounting your mics:

• They are stereo mics, so the left mic will need to be on the left side of your helmet, and the right mic on your right.
  * Otherwise, your audio experience won't match what's actually happening.
• The mics have polarity, so when adding lead wire, keep track of the positive and negative terminals of the mic.
  * If the mic does not work, you can de-solder the wires, switch them around, and re-solder them.
  * Bonus points: using Micro JST 1.25 male/ female connectors between the board and mics can make installation, uninstallation, and repairs easier. 

 

 

For mounting mics, there are other posts in FISD that cover that. Most TKs opt for two options:

• Make mounting holes under either side of the rubber brow gasket so the mics hide underneath the gasket
  Video by Matt Nelson here
• Make mounting holes behind the ear pieces, then use jeweler's drill bits to create miniature holes on the black ear stripe through which sound can travel to the mics. 
  Video by UKSWrath here

 

PRO TIP: bend the microphone leads at 90 degree angles before soldering and installation. This will be helpful when installing in either of the above locations. Also, protect and bare wires with shrink wrap or liquid insulation to keep your wires from contacting and shorting out.

 

Here's my own helmet for reference:

 

 

The Batteries

 

The kit comes with a battery holder for 3x AAA batteries. This is fine but can be bulky inside of a perhaps already-cramped helmet. Some people prefer regular AA batteries though because they're easy to swap if power runs out.

 

If you decide to stay with the 3x AA battery holder, do NOT fasten it to the back of the main board; instead, simply solder it to the board to alongside the board in the helmet. Otherwise, it will be too tall for it to be in the helmet while wearing it. you can even install it elsewhere int he helmet if you add more lead wire between the battery pack and board. Again, you can use JST connectors here to make installation easier, or to swap between batteries or USB power.

 

Speaking of which, if you have an old USB-A male cable lying around, you can easily cut this and splice this into the power leads on the board instead, and run the system off of 5V USB-A power. Then just choose any USB battery pack you prefer. For this, the USB-A connector has 4 wires, but you only need to worry about the 5V and Ground wires, usually red and black respectively matching what you would solder for the AA battery pack or to a JST connector.

 

 

PRO TIP: avoid battery packs that have auto-shutoff, since the hearing assist may not draw continuous power and such battery packs could shut off mid-troop.

 

Speaking of which, for those with battery packs with more than one USB port:

 

EM Noise and Battery Packs

 

This is fancy stuff, and if you have separate power supplies for your fans and hearing assist, you can skip to the next part. Otherwise, if you're interested, please read.

 

Running USB-powered fans off the same battery pack that's being used for a hearing assist can create EM noise for the listener, which is irritating and reduces the effectiveness of the assist. However, using a filter, like those used for old DSL lines, can mitigate or remove line noise.

 

 

I wrote about my own experience when I assembled and modified my Velleman some times ago (see "Phase 2" in the blog). I don't use the helmet bracket anymore, but all of the electronics concepts for the filter and assembly still apply.

 

There's an additional FISD post here that discusses it.

 

Keep in mind that using wireless mics can also introduce noise on a hearing assist. There aren't any easy ways around this since the mic lead wires will act as antenna that pick up this noise, beyond using RF shielding, which can be messy and cumbersome. I tried it, but somebody more clever than I might have a better approach. Your best bet is to switch to a wired mic. I use a pico mic and have never looked back.

 

Part 4 - Shrink Wrap or Encasing the Board

 

The easiest way to protect your work is to use 3" shrink wrap. Cut a section long enough to slip the board into, plus a little extra at each end, then shrink it with a heat gun or (hair drier on the hottest setting).You'll probably need to cut through the wrap for the headphone jack, and ensure that your mic lead wires pop out one side while your volume (gain) knob pop out the other. Add labels if you're feeling fancy.

 

 

 

There are also 3d Printed cases online, but the ones I've seen are for the assembly with the battery back mounted to the back of the board for the stock Velleman assembly, and wouldn't be useful in this application. But if I end up making an STL or finding one online, I'll append it to this how-to.

 

Part 5 - Mounting

 

 

We talked about mounting the microphones, but the main board and battery pack mounting is up to the wearer, so long as everything can connect when finished. My personal preference is having the knob close to the bottom of the helmet on the left or right side, so I can easily make volume/ gain adjustments without the knob being noticed.

 

As for how to fasten, most people use double-stick tape or Velcro. The latter can make it easier to remove if the assist isn't needed or repair/ replace if something breaks, especially if JST connectors were used in construction.

 

In my old tutorial, I mounted everything to a helmet bracket, but I later removed the bracket and mounted everything to the inside of the helmet with Velcro. Even later, I switched to mini blower fans, so I removed the assist entirely (the mics are still installed but not used).

 

Summary

 

It's all about time or money. There's nothing wrong with paying somebody to assemble a Velleman Super Stereo Ear for you, but if you have used a soldering iron before, or want to learn how to solder, this isn't a bad way to learn or practice. Either way, installing it can be the tricky part, but with a little extra care during construction, you can even make that a bit easier for yourself.

[SublimeBW[TK]]

Great info and I will be leveraging this weekend or the next to build out my Velleman kit.