My first electronics project, and it's a BIG one

Question

hello everyone this is my first post and i am very new at electronics. i am a lighting designer that designs and programs lights for concerts and other events. my preferred console that i use is a grand MA2 software and i have a on pc command wing. I have always found electronics fascinating and now that i have the following issue i have decided now is a perfect time to start! here is the project:

i am attempting to make a replica of this fader wing extension which retail cost over $3,500 easy. for my project i need to meet the following:

15 x 60mm linear slide potentiometers

60 x cherry MX white switches

USB type B connection to control the hardware via midi control.

the things i would like to do are this:

1) prototype and ensure that the entire system is working

2) program a stand alone pcb mounted microcontroller to control the hardware and software interactions preferably without using a arduino or similar thought this may be selfish?

3) have a proper PCB and Metal housing cut so that i am able to use it on actual jobs.

my big question is this:

what do you all recommend for me as a starting point. i can do the research on the potentiometers and the buttons thought those seem easy enough. have the microcontroller listening for the voltage of the potentiometers and for the buttons to send it 5 volts but i know there is no microcontroller that will have the whole 75 inputs i will need. do i use multiple microcontrollers? how do i hook them together? is there something i am missing in this project? thank you all for any input!

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* UPDATE *

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so i have discovered that there is a arduino Mega which has 50 odd connections not the full 75 i need but if there's a way to link the two and then have one USB out to the computer this may solve my issue of lack of i/o ports and dramatically reduce the complexity of this project.

jw0752 · Answer

Hi Chris, This is a quite ambitious project especially if you are going to try to design it yourself. The people who can design sophisticated systems usually go to school for it for years and spend most of their lives practicing and developing their skills. Though I have been active in electronics for over 50 years I would not attempt a design from scratch like this. On the other hand there is no rule that says you have to design it from scratch. Look and see if you can find an existing design that is open source and then try to build to those design specifications. As far as the inputs there are techniques that allow a microcontroller to expand its inputs but it is not as simple as it sounds. If I were going to attempt a project like this I would start with an existing design and then I would break it into parts that i could build and test independent of one another. Next I would hook the parts together into larger assemblies and test again. One factor that will help is that there is apt to be quite a bit of redundancy so that once you understand how to build one channel you will be able to replicate the other ones. If you do try to build this I hope you share your journey with us on the element 14 forum. John

genebren · Answer

Hi Chris,

This is where you might use a multiplexer A multiplexer is switch that can set to select one of it's inputs and connect it to it's output The output of the multiplexer would attach to one of the ADC inputs of the microprocessor(most likely also using a multiplexer to route one of the inputs to an ADC The select lines for the multiplexers(yes you might need a couple of mux's will be driven from the microprocessor to make the necessary selections A suitable part might be an 74HC4051D74HC4051D which is an 8 to 1 multiplexer

This is a pretty straight forward approach for reading several inputs with a single microprocessor. I have used this on several projects. The microprocessor could use a timer interrupt to manage all of the sampling of your controls (switches and pots). The logic could be something like this:

1st interrupt - drive all mux's to input 1, set ADC to first Mux.
2nd interrupt - start ADC
3rd interrupt - read ADC, set ADC to next Mux.
repeat steps 2 and 3 until all of the external Mux input 1have been read.
advance external mux's to imput 2, set ADC to first Mux.
repeat until all inputs have been sampled.

This process would run continuously sampling all of the pots and switches in the background. Once all of the data is collected and saved in RAM, the timer routine would set a flag the would indicate to the maim program that the data is ready to be processed.

I hope this helps!

Gene

cdog580 · Answer

basically all i am making is a rather large midi controller that send data to a computer via usb. i can map the signal that is being sent to the computer to any button on the software that i would like. i don't know if that helps. also i have found the arduino mega which has 50 something I/O s. this will let me reach the 75 i need IF they are able to be connected together so i can send all the button info through 1 usb to the computer. i am also assuming i will need a power supply of some sort inside the casing to provide power to everything including the LEDs for the buttons. so actually in theory i am going to need even more outputs because when you store data to a button it becomes brighter so i could link all leds per row in a parallel circuit but i would need outputs for them. meaning i would have to use two megas to get what i need. sorry this is me both asking a question and thinking out loud.

shabaz · Answer

I also agree with the sentiment expressed by everyone, to start in smaller chunks. From the URL you linked, it is unclear what the protocol is over USB to the PC software. Is it USB-MIDI, or is it some proprietary protocol between the PC software and the off-the-shelf controller? Also, even if it is MIDI, the traffic would need to be examined to see precisely what information is going over that link, like what channel, instrument number, etc I'm guessing. This is if you're looking for compatibility between that software and your hardware attachment. Some prototype code should be written (it could be done before even drawing a circuit or PCB), to simulate your input from a fader, and to send the value over the USB connection, receive over the USB connection and send to the DMX connection perhaps. I didn't really understand the flow, is it that the MIDI input is on the hardware device you wish to create, then send the data to the PC via USB, which manipulates it to control a lighting channel in conjunction with the fader setting, and then sends it back to the hardware you wish to create, to output over the DMX connection?

beacon_dave · Answer

You may find this book by Mike Cook of interest as it covers I/O and MIDI with the Arduino platform. https://www.apress.com/us/book/9781484217207 As for large numbers of inputs, don't forget that the Atmel ATmega devices as used in the Arduino support the I2C 'two wire' interface and you can get AtoD IC's that can give you the additional expansion you need. ADS7828 12-Bit, 8-Channel SAR ADC with Internal Reference and I2C Interface | TI.com

jw0752 · Answer

HI Chris, Some times the Arduinos can drive small loads like an LED directly but the best procedures are to have the Arduino drive an output stage with a transistor that in turn powers the LED or other device. You will have to determine the voltages and power requirements that are needed and then have a power source that is up to the task. The Arduino itself will run on 9 volts which it regulates down to 5 volts or 3.3 volts for actual processor and board operations. It looks like each output can source 20 mA. If all outputs were doing this you would need a supply that could deliver about 2 to 3 amps to be on the safe side. Be sure to check the detail specs on the Arduino as sometimes they will limit the number of outputs that can be sourcing simultaneously because of the danger of overheating the chip. By using external output stages the amount of current needed by the processor can be lowered and over heating is no longer a concern. If your output is just a digital one and not driving LEDs or other devices this would not be a concern. John

e14phil · Answer

Hi Chris I have previously watched this Arduino to Midi series. https://www.youtube.com/watch?v=DXhxdsGREsU I would suggest it as a starting point.

e14phil · Answer

.. side note... An Alternative to Arduino>Midi is: Arduino>HID>USB>MidiYoke>Midi https://www.arduino.cc/en/Reference/HID . That way you can have multiple input devices. Phil

genebren · Answer

Chris,

If you are using a microprocessor other than the Arduino, there are simpler approaches to programming. Most microprocessors can be programmed on the board, through a simple plugin programmer (usually a 6-pin header is all that is needed). This good to have, as it might take a bit of work to get it all working, so being able tr reprogram is a great thing. As far as the main processor, i assume that an arduino should work (I personally do not have a lot of ardunio experience).

Gene

beacon_dave · Answer

You can perhaps reduce the digital IO pin count required by arranging the switches in an 8 by 8 grid. That way with 16x IO pins on the microcontroller, you can read the state of up to 64 switches. You could also perhaps use external shift registers to reduce the pin count required without going to multiple micro controllers. Your LED's may be a bit harder though if you want to vary the brightness levels between on and off, as you are likely to want PWM enabled outputs for that (and not all digital IO is PWM enabled). Alternatively you could perhaps use pixel LED's, which would allow you to drive all 60 switch LED's from one or two IO pins.

beacon_dave · Answer

The Arduino Mega gives you 4x hardware USARTs as well, just in case you want to replicate the functionality of the DMX512 XLR outputs. Note that only 15 pins of the Mega 2560's IO can be assigned to PWM use to allow you to vary LED brightness. However as previously mentioned you could perhaps use pixel LEDs which have built in PWM control instead.

genebren · Answer

Chris,

Building your project as a series of smaller boards may also help. By having something like 5 boards of 3 pot and 12 switches or 3 boards 5 pots and 20 switches might make the project more manageable. These boards could be designed such that the pots and switches could mount directly to the boards (much less wiring). The boards could either have their own microprocessors or each be controlled by an Arduino. With a multiple board approach you would need to have a way to communicate between the boards (serial, I2C, etc) and one of the boards would have to host the USB to the PC (master, with the other boards being slaves).

A couple of things to keep in mind:

Only the the pot inputs need to be read by the ADC.
The switches can be configured such that they can be read by a standard I/O pin (digital).

Anything is possible, just break things down into simple steps. Start by using breadboards, an do simple things like reading a pot, or a switch. Only once you understand how to do each fundamental step should you begin to start laying out the bigger design.

Best of luck, and enjoy the journey!

Gene

beacon_dave · Answer

Yes indeed but you may need a few additional support components such as a crystal if not using the internal resonator.

Keep in mind that the likes of an Arduino Uno is based around the ATmega328 microcontroller with a few additional peripherals such as clock voltage regulator USB to RS-232RS-232 interface etc Perhaps take a look at this tutorial to see how to build one on breadboard

https://www.arduino.cc/en/Main/Standalone

The ATmega328 supplied in the Uno has an Arduino bootloader loaded onto it which then allows Arduino sketches to be loaded onto it via the Ardunio IDE to run you programs.

You can use an Arduino as a programmer to program stock AVR microcontrollers (which don't have the Arduino bootloader loaded). Take a look here for more information:

https://www.arduino.cc/en/Tutorial/ArduinoToBreadboard

The likes of the ATmega328 microcontroller can also be programmed outside of the Arduino IDE environment using something like Atmel Studio 7. This also gives you access to a much wider range of microcontrollers if you want the flexibility. Take a look at some of the other microcontrollers available in the AVR family:

Atmel AVR 8-bit and 32-bit Microcontrollers

The Arduino platform is however an excellent starting point for prototyping due to all the support (books, web pages, forums) that surrounds it.

My first electronics project, and it's a BIG one

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