Jaguar Prototype Testing

[Dan]

I used the CEL recommended 50ohm resistor to ground on the input and 100ohm resistor on the emitter output, I tried various resistances on the emitter output between 100ohm and 5kohm per CEL's datasheet and the larger the resistance I used past about 220ohms, the waveform on the output degraded to nothing but framing errors on the LA and a badly formed sawtooth waveform on xoscope.

The Ravage opto schematic doesnt have resistors on the emitter outputs? only 10K pull ups on the collectors and 2K4 pull ups on the tx and rx lines from the micro that go to the anode of the internal diodes. The emitter and cathode pins should directly connect to ground. I know the datasheet used this as their "timing test" circuit or some crap, but that is irrelevant to us. All opto circuits I have built have usually worked.

I am convinced that you dont need the emitter resistors at all, just connect them to ground as per the RavAGE schematic, just like the cathodes of the LED's are!

If you put it back in the same configuration as RavAGE, I would like you to change the 2K4 resistors to something low like 270R. This will allow 18.5mA to drive the internal opto diodes (LEDs). I think they need to be driven harder, as the existing 2K4 resistors only allow 2.08mA of diode current. (assume supply is 5V)

you can go as low as 220R, but I personally wouldnt go any lower. It should damn well work with that amount of current!!!!!!

Then we can work our way up with resistance and find our "sweet spot" in terms of amount of current required to drive the opto!

Any chance you may have gotten a crook opto IC? I cant open yet/havent looked at, your log stuff yet. But did you scope both opto's or just one?

[Dan]

our 10K pull-ups may also be a bit on the high side as well, you could try 270R ones in place of them as a different test too if you like? and work your way up to determine a sweet spot also!

Assume 5V, 10K only allows 0.5mA to drive our micro pin (CPU RX) or our FT232 IC pin (CPU TX).

If you try 270R ones in place of the 10K ones, then as per my last post, you will have 18.5mA -ish of drive. I am quite certain that will not damage our CPU pin or FT232 IC pin.

Awaits results........

[Fred]

You should NOT be putting values lower than about 1k on the CPU side, it could damage it. If you have stuff hooked up other than 4 pins, that's bad. I thought they only had four pins, though <checks datasheet> hmmm, the datasheet shows the rise/fall times as 5/10 micro seconds, which is about what we're seeing, so it's performing to spec. The spec isn't good enough. It needs to be quite a bit faster than that, and it really needs to be fairly symetric too so the on/off periods are not distorted, only phase shifted.

[Dan]

ok, 1K on CPU side then ! I forgot not all people have cpus to destructively test!

there are only 4 pins, but he added extra resistors and stuff.

Ok so they are working, but just not fast enough???

[Fred]

I must be confused! Let me reopen his file. Perhaps I misread the details. One second.

[Fred]

Yeah, I'm 100% right, they're just too low performance. Around 1us and symmetrical would be fine, so these are 10x too slow.

Fred.

[Dan]

these perhaps?

http://www.farnell.com/datasheets/609847.pdf

[Dan]

new thread created in RavAGE section for optocoupler selection . . . . not intending to hijack this one.

[Fred]

Damn it! I was :-)

[Dan]

LOL