craziest thing ever

[Dr_Doggy]

HELP! ohms law no longer applies!!!

I have a 4CH RF receiver that runs on 4-12v , wired to my PIC that reads the PWM(software), which works fine, but only when powered by the pickit(usb)!?! but, when i switch circuit to the 20C battery pack(regulated by the LM7805 to 5v), it loses its ability to go high ?!? but 5v pic still powers ok, and so does the receiver?!?

what could this be?
how do i fix?

 

[dpj]

I had similar kind of problem but in different application. In that case it was the amount of current supplied by the power supply was less than supplied by computer comm port.
Kindly see if adequate current is fed to your circuit with battery pack.

 

[Pommie]

What "loses its ability to go high"?

Mike.

 

[Dr_Doggy]

the RF receiver stops going high! but all other circuitry is responding ok (ie.. the PIC an other low current devices on it)

and the regulator chip LM7805 is regulated for 5V up to 1 amp, since these are RC high current batteries i am running from the actual source is around 7.4V and a supply current up to 25 amps

(if it helps the RFreceiver is a FUTABA R2004GF )

usb is what? 100mA supply, set @5v ( by pickit);; no way is it stronger...

 

[cowana]

What is the actual voltage measured after the 7805?

What do the power lines look like on a scope?

Andrew

 

[Dr_Doggy]

there is a (.01v 1HZ ripple + 5V) when powering up on the usb, but no prob on the LM7805(high supply),

also I should add that the RFreceiver still lights up red(for when the transmitter is off) and turns green(when TX is on).

EDIT....: I broke out the scope on to the data line, I watched PORTD.1 and detected the pulse on both supplies with NO DIFFERENCE, so it turns out that it is the PIC that is not working on the high source, The pulse on the scope never changed @portD.1 when i enabled the high supply, but the PIC18F4620, does not detect, ( it is not locking up, is running other subroutines, and starts detecting again when high supply disables)???

DURRING my test, i powered up pickit, detected high on pinD.1(TXoff), an a pulse(TXon), before and after enabling/disableing high supply

DURRING powering high supply everything works, detects high on pinD.1(TXoff), but when i switch TXon it should force low and starts the pulse, but instead it drops low properly but then cannot go high again, even when TX is off again, IT cannot go high again until high supply is switched off???


sorry for the headaches, but i' v had this problem for a while, on several other circuits,

 

[Sceadwian]

It sounds like a grounding issue. Do the receiver and the pic share common grounds when they're on the battery power?

 

[Dr_Doggy]

yes! all grounds are common, and vcc is all on the same bus aswell, with a 100uF capacitor in parallel, then @ the end is the LM7805 regulator

the only thing i can think it maybe is OSC1 and OSC2 pin are floating, but i got the clock set to internal(I THINK), so those pins should be disabled and not matter right? or should I tie them somewhere?

this is what my compiler says:

;Chip Settings
#chip 18F4620,8
#config MCLRE=OFF

BEGINING:
If PORTC.0 = 1 Then
Set PORTB.7 On
Else
Set PORTB.7 Off
End If
Goto BEGINING


THESE ARE MY CLOCK OPTIONS":

EC
ECIO6
INTIO67
INTIO7
RCIO

I think I just leave it @ default, right?

 

[Pommie]

The default, according to the data sheet, is external RC oscillator. Set it to INTIO67 and it will then use the internal one.

Mike.

 

[Dr_Doggy]

THNX, the datasheets get confusing for the PICs, and its really strange then that it still runs on default, unfortunately I set up the other clock mode but they both work the same

 

[Dr_Doggy]

thnx guys for all the help, I finally found it, something called CCP2 multiplexing was set to port C,E which caused 1/4 pins to go high and the rest low, so i switched it over to port B and it runs fine(until i need that pin!)

I just have one question about cpp2, since i just discovered its an actual interrupt is there a way i can disable it or make it active low(software(without inverter chip)), in mid programming, and maybe re-enable it too?