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Pinguino 26J50 kit
23-07-2013, 09:48 AM,
#11
RE: Pinguino 26J50 kit
Hi,
There is something wrong somewhere.
R must be chosen so that R = (Vin - Vz) / (Iz + Iout)
Iout = 200mA max. (cf. PIC Datasheet)
Iz = 80mA and 3.1V < Vz < 3.5V (cf. BZX85C3V3 Datasheet)
So R should be theoretically about 6 Ohm.
150 Ohm gives me 3.476V @ 5.2V,
Are you sure of your Zener diode ? Which one do you use ?
Can you try the same circuit with a 10kΩ load instead of the PIC18F26J50 ? Do you get the same values ?


(23-07-2013, 02:22 AM)Pinguino Wrote: The resistance solution was to increase the 150 ohm resistor to 150K. To arrive at this, I tried 330R, 470R, 750R, 1K, 2K, 12K, 18K, 47K, 82K, 100K and finally 150K.

150K produces these results:

o USB input voltage is 5V, 3V3 is 3.30V
o USB input voltage is 5.17V, 3V3 is 3.43V
It is easier to complain than it is to do, but it is better to do than it is to complain.
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23-07-2013, 03:53 PM,
#12
RE: Pinguino 26J50 kit
I used a 1N4728A 3V3 Zener diode which has very similar characteristics to the BZX85C3V3. The only variations in the datasheets being Iz = 76mA (cf 80mA) and Zz at Iz = 10R (cf 20R).

I'll try the 10K load test when I get a moment later this week.
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26-01-2014, 05:17 PM,
#13
RE: Pinguino 26J50 kit
I've just built one of these kits and after reading this topic I have installed an mcp1700-3302e/to regulator along with 2 small 100uF caps onto a 4 x 4 hole piece of veroboard. This board fits in the area between the USB socket and the PIC. I could modify the Kicad schematic and board layout (I've been using KiCAD for about 7 years) if this is OK. Please let me know and I'll have a go.
David.
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27-01-2014, 09:29 AM,
#14
RE: Pinguino 26J50 kit
It would be fine. Do you have the original Kicad files ?
It is easier to complain than it is to do, but it is better to do than it is to complain.
Reply
27-01-2014, 10:49 AM,
#15
RE: Pinguino 26J50 kit
(27-01-2014, 09:29 AM)regis Wrote: It would be fine. Do you have the original Kicad files ?

Are these the most upto date versions?

http://www.pinguino.cc/download/schemati...eric26J50/

Thanks.

David.
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27-01-2014, 12:10 PM,
#16
RE: Pinguino 26J50 kit
Yes, nothing has changed except the R2 value.
It is easier to complain than it is to do, but it is better to do than it is to complain.
Reply
04-11-2014, 09:55 PM,
#17
RE: Pinguino 26J50 kit
(23-07-2013, 09:48 AM)regis Wrote: Hi,
There is something wrong somewhere.
R must be chosen so that R = (Vin - Vz) / (Iz + Iout)
Iout = 200mA max. (cf. PIC Datasheet)
Iz = 80mA and 3.1V < Vz < 3.5V (cf. BZX85C3V3 Datasheet)
So R should be theoretically about 6 Ohm.
150 Ohm gives me 3.476V @ 5.2V,
Are you sure of your Zener diode ? Which one do you use ?
Can you try the same circuit with a 10kΩ load instead of the PIC18F26J50 ? Do you get the same values ?





(23-07-2013, 02:22 AM)Pinguino Wrote: The resistance solution was to increase the 150 ohm resistor to 150K. To arrive at this, I tried 330R, 470R, 750R, 1K, 2K, 12K, 18K, 47K, 82K, 100K and finally 150K.

150K produces these results:

o USB input voltage is 5V, 3V3 is 3.30V
o USB input voltage is 5.17V, 3V3 is 3.43V

Hi, if you choose R2=150 ohm, you have a problem with the current.
the current in R2 is 5v-3.3v / 150 = 0.0113 A this current - Iz is the board current, as you can see is too low to supply the board.
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