Power

[ArduinoPete]

Hello,

Do I need to power the Phduino with jp7 even when the arduino is
plugged into usb?

With out powering jp7 the ic2 gets very very hot. I have checked and
there doesnt seem to be any shorted out solder points.



Why is the jp7 marked +5v and -5 volt? Does it mean I need a
seperate power source and cant just split a line off of my 9volt input
with a lm317 adjusted to 5v?



And finally, I have it plugged into a arduino mega, this shouldnt
matter right?

[Carlos Neves]

2011/11/7 ArduinoPete <trevor....@gmail.com>

Hello,

Do I need to power the Phduino with jp7 even when the arduino is
plugged into usb?

JP7 is an output power for any low power purpose. The symmetric power for the operational amplifier is generated by the negative charge pump (MCP1121). The circuit works using the USB power or a +12V power supply.

With out powering jp7 the ic2 gets very very hot.  I have checked and
there doesnt seem to be any shorted out solder points.

Are you sure about the value of the resistors at the negative net of the circuit? A low resistor could be drain too much current from the negative charging pump. Check the polarity of the capacitors connected to the IC2.
 

Why is the jp7 marked +5v and -5 volt?    Does it mean I need a
seperate power source and cant just split a line off of my 9volt input
with a lm317 adjusted to 5v?

No. JP7 is a output symmetric power for any purpose. The operational amplifier TL072 (or the TL082) needs a symmetric power but the Arduino generates only +5V. The IC2 (MCP1121), negative charge pump, generates -5V from the Arduino +5V.

And finally, I have it plugged into a arduino mega, this shouldnt
matter right?

In fact, I never made this test because I do not have an Arduino Mega. You should check if the position of the pins are the same.


Carlos A. Neves

 

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[ArduinoPete]

First off,
Thank You,
for your time and making this public, and dealing with the hassles of
it being public(me! hah)


Ok , I verified all my resistors.
It occurs to me I have no clue on the difference between these 3
resistors is.

R11 1k R-EU_0207/10 0207/10 rcl 1
R12 1k R-EU_0207/7 0207/7 rcl 1
R13 1k R-EU_0207/2V 0207/2V rcl 1

I used the same +/-1% 1/4 watt 1k ohm resistor for all three....is
that ok?


I verified polarity of C11 and C12. All good

Pins match on the mega, I checked before I bought a mega, just thought
it worth mentioning.

Cap C12 May be my problem. I used a ceramic .10 uF. I thought 100nF
= .10uf. It might, but do ceramic capacitors have less resistance?
Maybe I need some other kind?

The cap I used for c12 is at this address

http://search.digikey.com/scripts/DkSearch/dksus.dll?WT.z_header=search_go&lang=en&site=us&keywords=478-3188-ND&x=0&y=0


I also have nothing plugged into the bnc port, I just wanna get it
running before I buy a probe.


Thanks!

[Carlos Neves]

2011/11/8 ArduinoPete <trevor....@gmail.com>

First off,
Thank You,
 for your time and making this public, and dealing with the hassles of
it being public(me!  hah)


Ok , I verified all my resistors.
It occurs to me I have no clue on the difference between  these 3
resistors is.

R11 1k R-EU_0207/10 0207/10 rcl 1
R12 1k R-EU_0207/7 0207/7 rcl 1
R13 1k R-EU_0207/2V 0207/2V rcl 1

I used the same +/-1%  1/4 watt  1k ohm resistor for all three....is
that ok?

Perfect.
 

I verified polarity of C11 and C12.  All good

Good.
 

Pins match on the mega, I checked before I bought a mega, just thought
it worth mentioning.

Ok.
 

Cap C12 May be my problem.  I used a ceramic .10 uF.  I thought 100nF
= .10uf. It might, but do ceramic capacitors have less resistance?
Maybe I need some other kind?

100nF is the same 0.1uF. A small ceramic capacitor is ok.
 

The cap I used for c12  is at this address

http://search.digikey.com/scripts/DkSearch/dksus.dll?WT.z_header=search_go&lang=en&site=us&keywords=478-3188-ND&x=0&y=0

It will work. Good.

I also have nothing plugged into the bnc port, I just wanna get it
running before I buy a probe.

No problem.

Thanks!

[Carlos Neves]

2011/11/8 ArduinoPete <trevor....@gmail.com>

>
> > With out powering jp7 the ic2 gets very very hot.  I have checked and
> > there doesnt seem to be any shorted out solder points.
>
> Are you sure about the value of the resistors at the negative net of the
> circuit? A low resistor could be drain too much current from the negative
> charging pump. Check the polarity of the capacitors connected to the IC2.
>
>

the two can type capacitors positive leads are both in the hole marked
+ on the pcb.  One of these positive leads is connected to the ground
plane, but it is marked +. is that right?

Right.

I noticed the -5v led is not on.

Hmmmm..... The MCP1121 could be damaged. Could you remove the MCP1121 from the shield and test it using a breadboard?
I put the leds to have a status of the symmetric power.
 

I used +/- 1% 1/4 watt resitors and I ordered them they were marked
individually and I took them out and soldered one at a time.  I will
verify them each by color strip though, to be sure.

[ArduinoPete]

That charge pump worked fine breadboarded per the schematic. It makes
-5 volts on the output.


Back to the pcb. I removed cap C10 (the one connected to 4 and 6) it
no longer got really hot.


I replaced cap c10 with the same cap I used on the breadboard. when I
turn it on with the new cap, it does the same thing, gets really hot
fast.


I guess this is obviously something in my soldering shorted or
something. Visually, nothing is shorting out or messed up, but it has
to be. The unused chargepump pins 1 and 6 I bent up so the are not in
the socket(in case they were accidently grounded.)


Maybe Ill start desoldering components, one at a time until it starts
working. any suggestions where to start?

[Carlos Neves]

2011/11/9 ArduinoPete <trevor....@gmail.com>

Remove the TL072 to test the TC1121. It could be damaged.


Carlos A. Neves