MJoy16 problems (solution?)

[Robb Bates]

The controls of my SimPit are based upon the MJoy16 circuit. I've built 3 of them and when they work, they work very well.

However, I believe the circuit is flawed. The fact that it is based upon a hack to make it work with USB means that it is flawed from the beginning. But, looking at the circuit and comparing it to the V-USB "standard" of using an Atmel chip to interface to USB, it doesn't look like it should work as well. For starters, it calls out 5.1V zener diodes (according to the partnumber) to pull the D+ and D- down to 3.3V levels. I replaced the 5.1V zeners with 3.3V zeners. They work, but with my new Windows 7 PC, the MJoy16 randomly disappears. I think this also might have something to do with the 2.2k and 4.7k voltage divider and/or the 82 ohm current limiter. The V-USB circuit doesn't have a voltage divider, it only has a 1.5k pull up and it uses 68 ohm current limiters.

Rather than replace the entire circuit, I removed the 4.7k resistor and so far (only one night) it seems to be working better. I'll post more if I find out more.

So for those who build an MJoy16 circuit and are having problems with it disconnecting, try that. No guarantees it won't fry your PC. I'm using it on a hub for now. Rather fry the hub than my PC.

The V-USB circuit also suggests using +3.6V zeners instead of +3.3V because of the potential voltage drop at those current levels.

More later.

Robb


For reference: http://www.obdev.at/products/vusb/index.html

 

[dnt462]

I have had no problems with it on windows 7, and my other problems had been fixed by grounding the potentiometers, and reprogramming the chip because I forgot to uncheck something. And all that was done when I was on vista

 

[Robb Bates]

Excellent. Did you use 3.3V zeners or 5.1V? And the rest was built according to the MJoy16 schematic?

If you do encounter any problems in the future, please post them.

How's your project working with Orbiter? Got it all tweaked and the buttons assigned, etc?

Robb

 

[tl8]

Instead of using zenors you might want to try a transistor or resistor type combination.
This image is what you want to do. The Arduino is all 5V while the SD card is 3V3. Also how are you powering your MJoy? It might be worth using an external power supply.

http://img441.imageshack.us/img441/2391/schematicuo7.jpg

 

[Robb Bates]

That probably won't work. The DI and DO on an SD card are unidirectional. The D+ and D- for USB are bidirectional.

The power may be a concern, but the only real power draw would be the current through the analog pots and the microcontroller consumption. Both of which are far less than the 500mA that an unpowered USB port can put out.

The V-USB project seems to have the right solution and the MJoy16 doesn't follow the same circuit. I'm pretty sure that's what the problem is. After I removed the 4.7k resistor from my circuit, I haven't had a problem. Only been running for two days, but so far so good.

Robb