other projects

I have made a new blog here for other projects such as analog2CV that works through AC coupled D/A converters and whatever else i feel like. it is Neutron-synth

Signal electronics are working!

I have tested all the parts together and they are working.
I only have one coil untill i settle on the exact configuration i need, but i have tested it on each string and amplifier channel.

I have tried a few different coils including hand wound electromagnets, relays, speaker coils, buzzer and bell coils. so far the bell coil works the best, it is 3 ohms and does not get too hot as long as you do not send it a full level signal for too long (that would never happen) and it imparts the attack of the sound in to the string which is the most important thing.

Unfortunately i dont think you can get these old electromechanical bells anymore.

also the pickup works and i can get the signal in to scope through the fostex VC-8

This is really good progress, and i actually got to hear some sounds :D (i just sent synth pulses from "miniscope" to the string, but it sounded cool. will record some soon.), it is looking good!

Next up will be to create a scope drvice which runs on the Pulsar DSP card. this will do all the hard work generating envelopes and processing the signal to be fed back to the strings

The  MIDI part will be done after that. For now i will just use a MIDI keyboard to emulate the guitar keys.

RCA adapter.

I am using this fostex VC8 as an analog /digital converter and ADAT TX/RX from the Scope card which will do the DSP processing.

I had a few choices.

1. run it "as is" outside the case with lots more wires all over the place.
2. Run it in the case with 12 seperate RCA plugs and their wires taking up space inside the case and making a mess.
   
3. In the case, Desolder the RCA adapters and run wires directly from the board,
4. In the case, Make an adapter so i can have only 2 ribbon cables running to the RCA jacks.and the VC8 is untouched so i could use it again.
   

I chose 4. it is just some 1/8 copper rod cut to length and soldered to the board. It worked out surprisingly well!

Amplifier carrier and Power supply

Just finished putting this together!
It is a carrier for the amplifiers, and they are easilly swapped out if i happen to blow one (which could happen when testing the string driver coils)

I just need to drill the heatsink and bolt on the chipamps with some nylon screws and mica washers. Each amp has been tested seperately and the circuit of the carrier board has been chacked for shorts and open circuits.

With this i can have neat cabling instead of a mess of in and output wires all over the place.

The board was made with the toner transfer system and is about as big as i ever would want to do again. some places the toner did not stick, and i had to draw the traces in with a sharpie, pretty low tech but it worked.

The heatsink is from heatsinkUSA.com which is a great source for DIYers. i have also used it for my little home theater box here. on [H]ardforums

Input Board

 

This is the input board, It has taken me a while to get all the things together which i needed to produce boards

I am using the "Pulsar PCB in a box" which is basically toner transfer from a laser printer, then transferred to the board using a laminator.

It has worked quite well, a couple of traces had to be repaired with a sharpie, but that worked fine.

First the board was designed on the computer.

then printed on special paper

the special paper and the board are run together through the laminator

then another stage with some green foil, which i also forgot to take a picture of.

Then the board was etched with ferric chloride.

The board is translucent white! it looks nice.

Holes were drilled on a Taig Mini lathe

And finally the parts were soldered in.

The LEDs were scavenged from a dead linksys router (for some reason LEDs in a bit of plastic cost almost 10 times as much as LEDs not in a bit of plastic)

All this board does is take the connections from the 13 pin guitar signal and MIDI in and route it to headers. the LEDs for the 13 pin will indicate the positive and negative power supply is working. the LED by the MIDI input is just a MIDI activity indicator.

The power for the 13 pin is needed because the Roland one i am using (and most other hex pickups as far as i know) has the preamp built right in , this power is usually provided by VG99 or whatever you are using the 13 pin system with.

Testing the FSR and spring

Here is a quick single key for testing.I will try various spring strength and positions for the FSR(force sensitive resistor) to see which gives the widest response.

I will also use this one to test the optical sensors used for keypress and velocity measurement.

So far it is giving about a 2 to 1 response with a fairly weak spring from a bike brake lever.
the wider the response the better, it is more likely i can use the FSR directly with the arduino rather than having to use external circuitry.

It should be ok with 1.25 volts range which would give me 8 bits of resolution out of the 10 bits on the arduino input.

I have completely changed the design of the key since i made that one and the rendering. both parts rotate around the same pivot point. it makes it easier to allign the optical sensors, and makes it more low profile.( it has to fit inside a guitar body.)

Case Modding

Well i managed to get the PC part in to a case now.
I bought a 2u rack mount box from ebay (very reasonable and quite nicely made)
The rear panel is from an old Pentium 3 server case. it took a bit of hacking up to make it fit properly.

Still some work to do, a front panel power switch and connect the power cord from the brick to the receptacle on the back.

There is quite a bit of space there, maybe enough for a mic preamp and a power amplifier.

But i dont need it for the project that is for another day.

New PSU for computer, measured wattege.

I got a DC-DC converter and power brick for the mini ITX.mini box now the only fan is the intel CPU fan which runs very slowly and barely makes a noise.(you have to put your ear next to it and only if no other computers are on) i have run it 24 hours without any sign of a problem.

The Total maximum power consumption under load gets barely over 60 Watts.
When running the Pulsar card DSP almost fully loaded and a few meters on the display moving. the total power (meassured with kill-a-watt at the plug) is 36 Watts.
(thats for the motherboard, CPU, PSU inneficiency, Pulsar card, and SSD) not bad! i will be happy to run this in a case with no external fan, just the CPU fan and the ventilation holes that are in the case.

The computer will live in one of these.
Inexpensive Antek DIY Project cases
The analog parts will go on the matching 1U case.

its been a while

I am waiting for a few bits i need to make a key and pressure work, meanwhile programming the new arduino mega. nothing very interesting to show a picture of though.

Layout changes.

I have made some changes To the layout.
The main reason behind this is because i was worried about having the amplifier power supply coming over a cable, If one rail was to become disconnected or short it is possible all the amplifiers could blow, or at least all stop working at the same time.

This way, if there is a bad connection it is between a speaker output and a "speaker" (the string drivers are not much different from a speaker, basically a coil.) and the amplifier chips have short circuit and open circuit protection. even if one blows, it is relatively easy to change a single one out rather than the whole lot of them.

The disadvantage is that there are now 3 cables, the speakon, the roland GK, and MIDI. before it was just MIDI and 2 nice light ADAT optical cables.also i dont think the speakon is really very optimal for real stage use because the guitar will be firmly attached to the controller box. However I doubt that *I* would ever be going on stage with this contraption!.

An advantage, though is that i do not have to cram so much stuff in the guitar, and the guitar will be lighter.

In other news, 3 of the amplifiers are completed and tested. (and the amplifier power supply) they worked right away, the boards are quite easy to build up.

For the power supply i found a nice torroidal transformer inside some horrible slimline "home theater in a box" which someone had thrown out.It has 13-0-13 secondaries which after rectification give +-17.5 volts.which is very nice for these amplifiers. they can produce 15 watts from that.

Also i found a server case which is almost suitable. It is aluminum, but way too long, i will have to do some modifications. mainly to make the hole on the correct place for the riser card, shorten the case to about half its length, and make a front panel..

How do i put this in laymans terms now? well i cant :D sorry hack a day internet sensation guidelines!

Key sensor circuit board

I have been working on the circuit board for the key sensors.
Iam using "expresspcb" I do not know if i will use their service yet, but probably will due to lazyness :)

For the mechanical part of the keys i plan to build 1 key myself till it is right, then have the set laser or water cut.



Dont know about electronics? check out "hack a day" or "instructables"  to see what people have done. Electronics has never been easier than it is now.

Key Assembly

Here is a rendering of the keys, you can see where the circuitboard holds all the optical and pressure sensors on one plane, which makes it easier to build.

The first optical sensor detects when a key has been pressed, and the second on is for measuring the velocity. the key then "bottoms out" on the first part of the stroke so you can feel it. you can then press down further to get "poly aftertouch" from the Force sensitive resistors under the main spring. It is not going to output "poly aftertouch" though each will be assigned a different MIDI CC, since it will be playing a custom DSP circuit it makes it more versatile, (each key could control something for that string, or all strings).

anyways, the main thing about this is that you can press the key through another 25mm or so after a note is played, so you can feel by the position what is going on, it is really hard to judge what you are doing with synth keyboard type aftertouch where you press down and do not really feel anything.

It will also be able to generate "pushes" on the string depending on how fast you are moving the key up or down, this will (hopefully) allow a controlled bowing of the string like a violin or other bowed instrument.

For people who dont know what this is all about. this is a "keyboard" but each key will "pluck" a guitar string electronically after you press a key there is additional movement to control the sound.