DIY Foot Pad - How to Make Sound With a Gel Heel Pad and Piezoelectric

Hello and welcome to the second part of my experimental mini-series of:

"How to make sound with XXX and piezoelectric"

In this part I'm building a foot pad out of a gel heel pad (insole).

• Gel Heel Pad
• Leather pieces (different types, thickness and color)
• Piezo Trigger
• Flexible Tube
• 6.3 mm Male Mono Jack
• Cable Connectors
• Wire Glue (contact glue, super glue)
• Cellular Rubber
• Soldering Tin
• Filament (PLA, black)

• Sissors/Cutter
• Screwdriver
• Wire Stripper
• Soldering Iron

• 3D Printer
• Trigger Module (TM-2)
• Instrument and Audio Cables
• Voice recorder (DR-05)
• Bass Drum Pedal (P-930)
• Cajon Beater (BE35)
• Headphones
• Mixer (Mix 8)

• Tinkercad
• Paint.net
• IdeaMaker
• Audacity
• Digital Audio Workstation (DAW)

Please take all necessary safety precautions while working with heat, sharp objects, electricity, vapors or resulting gases, noise, bright light and whatever could endanger your health.

2.1 The Concept

This has been the most surprising and cheapest pad I've made so far by using a gel heel pad (shoe insole). As the title reveals, it's meant to be played by foot.

2.2 The Shape

The shape is obviously dictated by the shape of the gel heel pad.

2.3 The Jack

During the building process (after glueing the saddle up leather and cellular rubber together) I saw this little cable connectors in an online store and immediatly wanted to try these out. I ordered yellow and black ones (red was sold out) and installed them to the jack cable and the pad as well.

This works really good and I can use the jack cable on other pad projects. Aside from that I don't have the big jack and jack plug directly attached to the pad or a cable dangle out of the pad while it isn't connected to the trigger module.

I've connected the cables to the jack by soldering.

2.4 The Piezo Disc

I've used the previously ordered Brass + Copper + Aluminium Wire Base Piezo Discs.

• Diameter: 27 mm,
• Thickness: 0.40 mm
• Wire Diameter: 1 mm
• Wire Length: 33 cm

2.5 The Assembly

Since I've so many leather pieces on my shelf I used these as the basis. I've

• glued the cellular rubber piece to the thick saddle up leather (contact glue)
• attached the cable connectors and the piezo disc to the saddle up leather (clear repair glue).
• glued the thin cream coloured leather piece on the back side (contact glue) glued the gel heel pad on the saddle up leather (clear repair glue).

I've waited 24 hours in each case to achieve the final setting of the adhesive.

I've designed (in Tinkercad) and 3D printed (on the Ender 2) some little cable connector holders in black PLA-Filament. I've glued the connectors into the holder (clear repair glue) for more stability.

After each process step I performed a sound test. As I've experienced lateley this does not protect a 100 % from failure (my first foot pad didn't worked out in the end) but it's quickly done and gives me a better feeling all over the building process.

The Trigger Module (TM-2) has two stereo trigger inputs. Via splitter cables the two stereo trigger inputs can be splitted into four mono trigger inputs to connect two more pads.

I've connected the foot pad, the knee pad and the two cymbal pads I've made in part 1 of this series to the TM-2 and the TM-2, speaker, headphone and voice recorder to the mixer via cable.

The sound was recorded by the mixers OUT to the line-in of the voice recorder (DR-05).

Well, it was meant to be played by the heel in the frist place. But I couldn't generate a continues, steady beat. Adjusting the threshold only led to multiple or no triggers. I was wondering if the piezo disc was broken like the one before. I adjusted the pad range, threshold and sens within the TM-2 over and over again - without receiving the hoped-for performance. Playing the pad by hand went well but when layed down on the floor and played by heel it sucked.

I presume, the striking surface of my (indistinct moving) heel compared to a beater is too big and soft and couldn't create the precise and consistent pressure point to the pad.

I decided to attach the pad to my single bass drum pedal P-930 with a cajon beater BE35 (because of its soft foam beater head). This went much better although the angle wasn't perfect because it wasn't originally made for this kind of attachment. In hindsight the idea to go for the cajon beater sucked as well because of the miserable angle the large top nut left marks on the gel heel pad surface.

... for reading, watching and paying attention.

The surprising part has been the fact, that I couldn't find a setting to play the pad by heel and ended up playing it with the P-930. This wasn't predictable to me and I'm glad I found an "O.K.ish" solution and will replace the cajon beater with a standard one.

In the whole designing process the hardest part is the jack connection in my opinion. The jack and the jack plug/cable are heavy and my selfmade pads are very light (compared to my professional manufactured pads). But detecting this little, light cable connectors will give me more freedom in designing for the next projects, and there are at least two more to come - so please stay tuned.

Please let me know if you've made one as well and/or if you have a solution to play this properly by heel.

Hopefully Auf Wiedersehen in one of my next instructables.