If you are into customizing or building 3D printers, you might be using an “MKS Gen” control board. I am building a HyperCube from Tech2C and I have chosen to use that card. Correctly installing a Z axis proximity sensor was a good learning process fo me, so I thought I share my experiences, it might be useful for others.

The idea of a standard mechanical end stop is, that a signal circuit is open (thus, is not giving a signal) until the print head would travel to one end of its route (determined by the physical dimensions of your printer). Which point it hits the mechanical switch and closes (triggers) the signal circuit. This signal then picked up by your control board and triggers certain functions, instructed by the board’s firmware.

You might want to use a metal detecting proximity sensor to replace the mechanical switch on the Z axis of your printer. There are several reasons to do that, one of which is the possibility to use it for the auto level function of your firmware (in my case that is Marlin). I have touched the subject of the available alternatives of a mechanical switch in one of my earlier posts.

One of the many alternatives of a metal detecting proximity sensor is the one named “LJ12A3-4-Z/BY”, which is quite imaginative if you think about it. This sensor is a PNP sensor. PNP stands for “positive-negative-positive”, that basically means that it is continuously giving voltage in a signal cable, if it is not close to metal and gives zero voltage when it is close. Our metal bit is, of course, the print bed.

That would be OK with most control boards (parameters have to be changed in Marlin), but the MKS Gen card’s hardware prevents the use of this type of sensor. As the device only cost about £3 ($4-$5), the obvious course of action would be to order a NPN type sensor (which would give logic “LOW” voltage while it is not triggered and logic “HIGH” voltage when it is triggered) and instal that with only a small modification.

The device requires a minimum 6VDC in order to function properly. The end stop socket on most Arduino based boards only provides 5V. However, it can be powered directly from the power supply, which gives 12V. In that case, the signal will be too strong to feed it back to the board. So you can either use a voltage divider or a diode to step down the strength of the signal.

A good explanation by Tech2C of that can be seen here:

Most “DIYers” like me, however likes the challenge (I guess), so instead of buying another one, I have spent at least half a day with building a simple circuit, using a 2N3904 transistor to reverse the signal, with the advantage of having that signal suitable to feed directly to the board.

Here is the story in pictures:

I am not going into details about the explanation of electronic principles about components, this is more of a guide how to get around of the PNP sensor problem. If you are interested more about the workings of transistors, etc, I will include a reference and recommended links list at the end of this post.

My aim is to reverse the signal pictured above and decrease its strength when it is logic “HIGH”. I need that it gives a “HIGH” signal when triggered and “LOW” signal when it is not.

Here is a simple circuit to build in order to do that. The idea comes from here, I have just draw the schematic in KiCad instead of using the quality hand drawing.

And there you have it! The modification is successful, the sensor now ready to be used in my/ yours/ anyone’s set up.

References and recommended links: (I have no affiliation to anything here, just pointing towards things)

Buy a LJ12A3-4-Z/BY and have the opportunity to spend at least half a day solving a problem, which should not be a problem at the first place!

Read the Art of Electronics. It is the bible of all electronics books.

Read into electronics, but a bit more digestible way.

Build a HyperCube.

Buy a lot of 2N3904 transistor. You can use them to build interesting beginners electronic projects.

Zen3d – Run by a friend, read it if you want to know about DIY 3d printer building or if you want to learn Hungarian – good practice.

Write me an email, if you need help in anything in this post.

And so than, I was hooked. My interest in electronics sparked (bad pun) again a couple years ago, when I bought an Arduino microcontroller out of interest, than I was introduced to 3d printers by a friend, than I have started to mess around with ICs and bought a 1000 books on the subject. All these eventually led me to be fascinated about electronic sound synthesizers. Why? Erm, “dunno”, I think it is pretty cool to make sounds out of pieces of electronic components.

One of my first projects was an Atari Punk console. The original design was published in a Radio Shack booklet, the “Engineer’s Notebook: Integrated Circuit Applications” in 1980 by Forrest Mims. He simple called it “Sound Synthesizer” or “Step Tone Generator”, but most popularly it is known as Atari Punk Console because the sounds it makes, resembles of the old Atari 2600 game console.

It is based on a very famous (in electronics anyway) IC chip, named “555”. In fact it is based on two 555 chips or alternatively one 556 (which is two 555 chips integrated together)

This little IC is around since the 1970`s and it is the current holder of the world record as the most numerous IC produced of all time.

The 555 is also called a “timer” or a “timing IC” as it can produce electronic signals in equal intervals. It produces a square wave (shaped) signal. The chip itself has 3 core set ups (monostable, astable, bistable) and it can be found in thousands of devices from toys to space crafts.

I will not going through in details how the IC is working, there are plenty of publications can be found online about that.

The IC is can produce a square wave shaped signal, which ultimately gives the distinctive sound it makes and which explains why it sounds like an old 8 bit game console.

 

In the basic Atari Punk Console, one chip is set up in “astable” mode and that drives an other 555 which set up in “monostable” mode. Alternatively, one 556 chip can be used too but the theory how the machine works is exactly the same.

Here is the schematic which I have designed, based on other DIY punk consoles can be found online. My version has 6 variable resistors (potmeters), four are which functions as filters using an other two 555s and you have the standard knobs for pitch and for tone.

The box has an audio output. I am using 1/4 jack sockets, but you can use your own preference, like a 3.5mm or banana jacks. The audio socket can be replaced by something like an 8 ohm direct speaker, maybe with a simple little amplifier such one based on an LM386 Op-amp

There is a CV (control voltage) input, wired to an other 1/4 jack socket. I am using this with a DIY 8 step sequencer (I will make a post about it at some point).

As of power, it has a standard DC power socket for a 9V power supply and an on/off switch.

BOM:

Variable resistors (pots)

• 50k * 4
• 500K * 2

Capacitors

• 0.01uf * 3
• 0.1uf * 1
• 3.3uf * 2
• 10uf * 1

Resistors

• 1K * 3

ICs

• 555 * 4

You can find the .stl files for printing the box on my thingiverse profile.

https://www.thingiverse.com/thing:3658579

 

One might asks, – What can you do with it? – Well, anything you want. It is possible to hook it up to a sequencer, a filter, VCV rack through a jack-usb cable, etc. In all honesty, it is obviously not the nicest sounding musical thing you can imagine, but nevertheless you can have some fun with it, it is a great learning process and relatively easy to build. Here you can see it is hooked up to a sequencer and a tacky old “Behringer Tweakalizer”, recording in Audacity through a laptop.

 

 

Here is a 2 minutes sample of some of the sounds this box can make on its own:

https://api.soundcloud.com/tracks/630880506