Re: [PIC]PIC18F4550 board - is my schematic correct?

make
*R4,r1=1K
USE c1 and c2 =15pF or less or change oscillator to 8MHz

Check the datasheet for VUSB capacitor value
ADD some capacitor on 5V for regulation 10/1uF near the supply (usb
connector).

Remaining all are safe,

*
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Re: [EE] Piezo buzzer as a sensor connected to the uC ADC

ivp ha scritto:

> I use 15 of the attached as input pads for a MIDI drum kit. The pot
> is a sensitivity control. The opamp is wired as a peak detector with a
[...]

Yep, I'd use an op-amp - as they used to do in the old times ::)

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Re: [PIC]PIC18F4550 board - is my schematic correct?

Barry Gershenfeld ha scritto:

> One more firmware note.  This may have changed in later releases, but the
[...]

Just a couple of notes, Barry:
yes it was the old 16C software - recent ones did "improve" this :)

And , as for the detection resistor, it used to be D- for low-speed,  D+ 
for full, and I'm not sure about high. And, on newer parts, it's no 
longer added externally, rather available on chip and software-selectable.

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Re: [PIC]PIC18F4550 board - is my schematic correct?

>And , as for the detection resistor, it used to be D-
>for low-speed,  D+ for full, and I'm not sure about high.

That is correct, and then for high speed, the device starts as full speed, 
and then negotiates high speed mode, if it is capable of it. 

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Re: [EE] Piezo buzzer as a sensor connected to the uC ADC

The peak detector (either based on op-amp, or without it) is certainly
needed, as the pulse from the disk is very short (see attached oscillograms).
The only problem is that I don't know if the polarity of the pulse is
warranted. The two disks I've measured provided the positive pulse at the
silver contact with brass connected to ground, when laid brass side up and
hit from top.

I wanted to be prepared for reverse polarity as well, and that's why I've
used the Graetz bridge.

If I could be sure, that polarity of disk is always the same, I could
significantly simplify the circuit.

I attach two pictures. The first one is the output from the unloaded disc
(see the very high voltage - ca. 25V).
The second one is the output from the circuit I've presented in my first
post (with Graetz bridge, capacitor 330nF and resistive load ca. 43k).
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Re: [EE] Piezo buzzer as a sensor connected to the uC ADC

>> clamping diodes on the ADC input are sufficient protection measures?
>> Is there any latch-up danger when someone hits the piezo too strong?

I would suggest you add external Schottky diodes, particularly on the
ground rail (anode to 0V, cathode to PIC pin), if you're concerned
about transients. Something small will do, eg BAT46. Although what
you and Bob suggest appears to isolate the piezo from the PIC fairly
well
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Re: [EE] Piezo buzzer as a sensor connected to the uC ADC

> The only problem is that I don't know if the polarity of the pulse is
> warranted

That's probably a fair point in a controlled (ie you built it) situation

> I wanted to be prepared for reverse polarity as well, and that's why
> I've used the Graetz bridge

Yes, you'd have to account for accidents, eg the stand falls over and
the piezo is hit from behind, or resonance/bounce-back of the mounting
plate causing a negative-going pulse
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Re: [EE] Piezo buzzer as a sensor connected to the uC ADC

ivp wrote:
>>> clamping diodes on the ADC input are sufficient protection measures?
>>> Is there any latch-up danger when someone hits the piezo too strong?
> 
> I would suggest you add external Schottky diodes, particularly on the
> ground rail (anode to 0V, cathode to PIC pin), if you're concerned
> about transients. Something small will do, eg BAT46. Although what
> you and Bob suggest appears to isolate the piezo from the PIC fairly
> well

Preventing latchup is important, but I don't clamp anything to the
supply rail, I don't want transients pumped into it that could affect
the ADC conversion as it's taking place. I want really clean rails on
any ADC.

Cheerful regards,

Bob
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[EE] Question - PICS in space?

I just found this (http://opensat.cc) guess some people already know about it,

but i'm not an atmel expert as you can expect, so i wonder if any one know about using
microchips chips in space, in satellites, issues relate with it and all the electronic system
that it involves?

Saludos :)

Cristian Pauñ
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Re: [PIC]PIC18F4550 board - is my schematic correct?

Thank you all for your help!

>Am I doing that, according to my schematic?

Quoting myself here... I didn't realize I had VBUS connected to VDD in my
schematic, and it is now fixed.

I've made a lot of changes to the schematic and especially to the PCB,
notably:

   - Grounded the PGM line.
   - Disconnected VBUS (voltage line from the USB cable) from VDD.
   - Changed LED resistors from 390 to 1K resistors (if the LEDs are not
   bright enough, I can always change back to 390 Ohm, right?).
   - Changed the crystal's capacitors from 22pF to 15pF.
   - Added 1uF and 100nF capacitors close to the power connector for
   stability.

Schematic:
http://www.roboticsguy.com/images/misc/pic18F4550-schematic-r3.png

PCB with parts labeled:
http://www.roboticsguy.com/images/misc/pic18F4550-pcb-board-labeled.png

One other thing that several people have mentioned, and which does not seem
to be agreed upon, is how to detect when the USB module is plugged in. I
found this image in the 4550 datasheet:
http://www.roboticsguy.com/images/misc/figure-17-11.png

Should I add the sense resistors, as shown in the above picture? Is it even