S2Kman

I am already aware of the solution available for the control of a deck via the S2000s dash controls, the unit that converts the key presses to infra-red commands. However, I have never been sold on that solution and have been wanting a wired solution. I am working on building my own direct cable interface that will plug into the Dash control circuitry and then into the 'Remote Commander' port on the back of Sony decks.

My solution to the problem is based around an Atmel AVR microcontroller that has a built in 10 bit A-D converter. I am using the A-D converter to read the voltage drop accross the dash control circuitry and 'detect' a button press. I have the circuitry figured out for this and am about 50% done with the software to do all of the S2000 button sensing.

The difficulty is on the Sony side. I know the Sony remote commander also uses a bunch of resistors tied to switches similar to the S2000 dash controls, however I am not sure what mechanism it reads the resistance values with. I am trying to determine what type of circuit I should use to connect to the sony, but I'm not sure. I was thinking that the Sony head units might also use an A/D converter to detect a voltage drop, but they might just as easily be using a capacitor charge/time to detect the resistance.

If the Sony uses an A-D converter to detect the voltage drop accross the resistors, I could have my microcontroller re-produce these voltages via a D-A, I might even get away with PWM charging up a cap. If the sony is using cap charge/time it gets more complicated. I know I could use some relays attached to resistors, however I was trying to avoid that.

Any ideas? Is there a way for me to digitally control some device to vary the resistance of the device? That would be easiest, a sort of Digital to Resistance converter. A digitally controlled Potentiometer would be perfect, does such a thing exist? (something other than a servo motor attached to a pot)

I'm more of a software guy than a hardware guru.

bbsilver

[QUOTE]Originally posted by S2Kman
[B]I am already aware of the solution available for the control of a deck via the S2000s dash controls, the unit that converts the key presses to infra-red commands. However, I have never been sold on that solution and have been wanting a wired solution.

MacGyver

S2kMan,

You might want to get into contact with almilli...I was helping him debug a circuit he put together a few weeks ago to do just such a thing with Sony head units (of which we both have). I don't know what his progress is like, or if he is even going to finish the project, but it's geared more towards discreet components rather than a microcontroller. I handle software and hardware equally badly, but in this case, the discreet case seemed the simpler solution, especially considering our target use (Sony) won't change.

As for the digital potentiometer, yes they exist, and are actually quite reasonable in price. They generally have a serial programming interface, and I've found them to be quite useful for certain types of projects, this type included.

Let me know if I can be of any assistance...

S2Kman

MacGyver,

Thanks for the info on the digital pots. I looked them up on yahoo and downloaded some spec sheets. They sound like exactly the type of device to use to make this a simple project. My major concern is that make sure that this circuit works with a variety of Sony decks, and I don't think I can be certain that they all do things the same way even though they all work with the same Remote Commander. They may vary from deck to deck in the way that the resistances are read.

For the digital pots, I ordered some samples off of the Dallas web site, but I can't find any distributors who carry any of them. I checked Digi-key, All-American and Arrow. Arrow had a few Xicor part numbers, but not any of the ones that would be useful to me. I'm thinking that the 256 or 1024 tap varieties are the most likely to fit the bill. Xicor had 1 part number that was a 100K 256 tap, but it was a quad and was $12. Seems a bit steep. The single pot versions were reasonably priced $3-$5 but not available. Dallas makes a couple of 256 tap versions (ordered some samples of these), and Xicor has both 256 and 1024 tap versions. The Xicor X9119 looks like the best bet, it is a single pot, 1024 wiper, linear 100K ohm, 2 wire interface. That gives about a 100 ohm resolution if I can find that part. Arrow shows this part at $5-$7 but not available. Any idea what supplier might be able to sell low-quantity of this part? Once I know the required resistance values for the Sony I can determine which part will work the best.

One other thing. Did you produce a button/resistance map with the work you were doing for the discreet circuit? I haven't been able to find a Sony Remote Commander at any of my local audio shops. If I can't find out the resistances, I think I can order one from the Sony web site and then I can ohm it out myself, but if you already have a map, it will save me the $40.

I never even thought about this project with discreet components, I'm just not strong enough in hardware to have a chance at success that way. I also want to be able to add some additional features to the unit once I get the basics working. A couple of ideas I have:
1. Press and hold S2000 dash control to access secondary function for that button
2. Auto volume step up/down based on vehicle speed and top/up down condition.

Right now I am focusing on getting the Micro to be able to memorize and recognize the various S2000 buttons. The Micro I am using has non-volatile internal EEPROM for storing data, so I am making it programable. This should also ensure that it will work with any S2000 since none of the data points will be hard coded, but rather 'learned', therefore allowing for resistance tolerance variances and such. If you are interested in using the code/circuit that I come up with, I'll be happy to post all the details here on the board or on my web server.

RandyP

The Sony remote does not seem very complex considering that the PAC can read its signals with this simple mod:
http://www.go2pac.com/misc/rmx2s.html

MacGyver

S2k,

I'm surprised Digi-Key didn't have want you wanted...I could swear they've had those parts in the past. If you can find a part that has fewer taps, but a lower total resistance for a cheaper price, go with that...I believe the Commander has a total resistance of close to 50 kOhms for the largest resistance button. On second thought, maybe having the leeway of 100 k isn't so bad, and 100 Ohms is a high enough resolution.

Almilli completely mapped out the Commander, so ask him if he'll provide you with the mapping. If not, I'll see if I can dig something up...

If you plan on adding functionality over and above the stock controls, then a microcontroller is definitely the way to go. I don't have any experience with the Atmel controllers, but I've been a fan of the PICs from MicroChip ever since I wrote an RTOS for Polaroid. They're RISC chips, so the instruction set is quite small (but surprisingly powerful)...in fact, I only used about 8-10 instructions for the majority of the code. The core was a couple hundred bytes...I think the switch debouncing routines were larger than the core was. Oh, and the PICStart development system is pretty darn cheap, too. Incidentally, they use a PIC16C715 in the PAC units. Great minds think alike


Side note to all...I've updated my webpage with potential issues and solutions for the PAC unit.

S2Kman

MacGyver,

I was surprised digi-key didn't have it too. I wish that they had a better search feature, finding parts on their web site isn't very easy unless you know all the possible part numbers you might be looking for.

I chose the atmel microcontroller over the Microchip because it seemed to be more flexible than the Microchip stuff. Built in support for in circuit programming in most devices, 90% of the instructions execute in 1 clock cycle as opposed to 2 for the Pics, and a wide range of easily available configurations. The Atmel AVR's are also RISC and the instruction set is powerful. The development kit for the AVR was only $95 and included a nice development board and 3 chips to start out with. This is my first real project with the AVR, I've been using basic stamps for small projects for a while. Assembly was scaring me off, but it's actually a lot better than I thought. In many respects I think it is easier than programming the stamp because you can do whatever you want with no constraints, plus you can do it a LOT faster and with very accurate timing.

I e-mailed Almilli to see if he can provide any info on the commander. Thanks!

almilli

s2kman just emailed me. I'm pretty far along in the project. it's actually been sitting in my closet for a while though because I lose motivation. I'm just having problems reproducing the resistances for the sony unit. The NPN transistors are completely throwing it off. I did find a possible alternate solution to the NPNs using an IC (quad SPST analog switch).

Maybe some extra help from s2kman will help it get finished. We are both in the same city after all.

David

MacGyver

S2Kman: If memory serves, the only main instructions that take two cycles are jumps. Besides, who cares if it takes 50 cycles to finish an instruction, as long as it does those 50 cycles sufficiently fast, right? I'm not sure about in-circuit programming for the PIC, but adding that feature wouldn't be much different than the Atmel...any chip you choose will have to have the support hardware on whatever board you design to gain that feature...unless they were nice enough to place it all onchip. Digi-Key website is a pain in the ass, download the PDF version of their catalog and print it out...much easier.

almilli: The analog switches will certainly avoid any problems with collector-emitter drop. Keep me posted as to what you guys put together.

almilli

Sure thing. I talked to S2kman on the phone and sent him the diagrams for the sony remote. He's still working on programming the microcontroller for the correct values. I might go get that IC this weekend and see if I can get it working.

David