78L05

[Tuurbo46]

Hi

Im currently using a 78L05 chip to power up my PIC 16C773 and my 231CPD
driver/ reciver chip. The circuit functions ok when running, but the circuit
is real hard to boot up. When the circuit is connected to Hyper-terminal
when phalse boots occur junk comes through.

The 78L05 is fead with 12V DC on the input and has a 10uF polarised cap
accross this input to ground. When i disconnect this cap the booting becomes
impossible and the junk on hyper-terminal is worse. Therefore if i say put a
100uF cap in place of my 10uF, would this solve all my problems? If so what
is the maths behind it, or is it just a plug and play theory?

After reading through a few of my monthly issues of practical electronics, i
notice that most of the circuits that they build us 100uF! Is this the
reason why they use them?

Cheers Turbo46

 

Tuurbo46 wrote:

The 78L05 is fead with 12V DC on the input and has a 10uF polarised
cap
accross this input to ground. When i disconnect this cap the booting
becomes

What is the ripple on this "12V DC" input?

 

[Tuurbo46]

I think it has zero ripple because it comes from a 12V DC battery. It a
small version of a motorbike battery.

<larwe@larwe.com> wrote in message
news:1107890114.934722.141210@g14g2000cwa.googlegroups.com...

Tuurbo46 wrote:
The 78L05 is fead with 12V DC on the input and has a 10uF polarised
cap
accross this input to ground. When i disconnect this cap the booting
becomes

What is the ripple on this "12V DC" input?

 

[Anthony Fremont]

"Tuurbo46" <alex@beale55.fsnet.co.uk> wrote

Ur um, the thing to work please. lol

Then put a .01uF cap on the output and maybe a 1uF as well. I wouldn't
use more capacitance on the output than on the input.

Add seperate bypass caps to the PIC unless you like allot of mysterious
resets. PIC chips are fussy about how fast Vdd ramps up too. If it
comes up too slow (>100mS), then the PIC won't come out of reset.

BTW, please don't top post.

 

[John Fields]

On Tue, 8 Feb 2005 19:29:55 -0000, "Tuurbo46"
<alex@beale55.fsnet.co.uk> wrote:

Ur um, the thing to work please. lol

---
Tell us what else you've got hooked to the battery, where it's hooked
up and how long the wires are, and how long the wires are going from
the battery to the regulator. Also, do you have anything else hooked
to the +5 side of the regulator other than the 2 chips you already
mentioned?

--
John Fields

 

[Mark Jones]

Tuurbo46 wrote:

I think it has zero ripple because it comes from a 12V DC battery. It a
small version of a motorbike battery.

And does this motorbike battery have a charger? If it does, does the charger
put out any ripple? Any vehicle is going to have horrendous spikes from the
charging system. Ripple from these chargers will go straight past the battery
and cause problems unless designed around.

 

[Rich Grise]

On Tue, 08 Feb 2005 19:07:07 +0000, Tuurbo46 wrote:

Hi

Im currently using a 78L05 chip to power up my PIC 16C773 and my 231CPD
driver/ reciver chip. The circuit functions ok when running, but the circuit
is real hard to boot up. When the circuit is connected to Hyper-terminal
when phalse boots occur junk comes through.

The 78L05 is fead with 12V DC on the input and has a 10uF polarised cap
accross this input to ground. When i disconnect this cap the booting becomes
impossible and the junk on hyper-terminal is worse. Therefore if i say put a
100uF cap in place of my 10uF, would this solve all my problems? If so what
is the maths behind it, or is it just a plug and play theory?

After reading through a few of my monthly issues of practical electronics, i
notice that most of the circuits that they build us 100uF! Is this the
reason why they use them?

In the time it took you to write this, you could have already put in the
100 uF. Why do you hesitate?

Good Luck!
Rich

 

[Rich Grise]

On Tue, 08 Feb 2005 17:42:59 -0500, Mark Jones wrote:

Tuurbo46 wrote:
I think it has zero ripple because it comes from a 12V DC battery. It a
small version of a motorbike battery.


And does this motorbike battery have a charger? If it does, does the charger
put out any ripple? Any vehicle is going to have horrendous spikes from the
charging system. Ripple from these chargers will go straight past the battery
and cause problems unless designed around.

In which case he also needs a hash choke.

Cheers!
Rich

 

[Rene Tschaggelar]

Tuurbo46 wrote:

Hi

Im currently using a 78L05 chip to power up my PIC 16C773 and my 231CPD
driver/ reciver chip. The circuit functions ok when running, but the circuit
is real hard to boot up. When the circuit is connected to Hyper-terminal
when phalse boots occur junk comes through.

The 78L05 is fead with 12V DC on the input and has a 10uF polarised cap
accross this input to ground. When i disconnect this cap the booting becomes
impossible and the junk on hyper-terminal is worse. Therefore if i say put a
100uF cap in place of my 10uF, would this solve all my problems? If so what
is the maths behind it, or is it just a plug and play theory?

After reading through a few of my monthly issues of practical electronics, i
notice that most of the circuits that they build us 100uF! Is this the
reason why they use them?

How about having a look at the waveforms with a scope ?

Rene
--
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net

 

[j.b. miller]

Gee I've used PIC for years, and as long as I enabled POR (Power On Reset)
I've never had a problem even with 'interesting' power supply
configurations. I always have at least a 100mfd/25v cap on both in and out
of the 78L05 as well as .1/25 disk caps.
Jay

 

[Anthony Fremont]

"j.b. miller" <invalidjbmiller@cogeco.ca> wrote in message
news:2HrOd.6180$Sx6.951146@read2.cgocable.net...

Gee I've used PIC for years, and as long as I enabled POR (Power On
Reset)

You must mean PWRTE. ;-)

I've never had a problem even with 'interesting' power supply
configurations. I always have at least a 100mfd/25v cap on both in and
out
of the 78L05 as well as .1/25 disk caps.
Jay

I didn't have any problems either until I started working with the
"nanowatt" 16F88.

 

[Anthony Fremont]

"R.Lewis" <h.lewis@connect-2.co.uk> wrote in message
news:36v3l6F536atiU1@individual.net...

Usually no problem if the RC on the boss 'MCLR' reset pin can be
made to
hold the PIC reset for say 5-10 seconds but if a 12C... type PIC is
programmed to use MCLR as GPIO, then the internal power up
timer/brownout/reset etc, just loses it.
regards
john

Interesting that bit about the internal MCLR being 'dodgey'.
Could you explain further?

I don't think he means that it's flaky. IIRC, it's just a simple
pull-up resistor with no cap internally, consequently no time delay.

IANEE

 

[R.Lewis]

"Anthony Fremont" <spam@anywhere.com> wrote in message
news:KVvOd.33114$sr1.1873@fe2.texas.rr.com...

"R.Lewis" <h.lewis@connect-2.co.uk> wrote in message
news:36v3l6F536atiU1@individual.net...

Usually no problem if the RC on the boss 'MCLR' reset pin can be
made to
hold the PIC reset for say 5-10 seconds but if a 12C... type PIC is
programmed to use MCLR as GPIO, then the internal power up
timer/brownout/reset etc, just loses it.
regards
john

Interesting that bit about the internal MCLR being 'dodgey'.
Could you explain further?

I don't think he means that it's flaky. IIRC, it's just a simple
pull-up resistor with no cap internally, consequently no time delay.

IANEE

Thanks for that but I thought I could drag from memory that someone wrote

that (on the nanowatt?) PIC's you should use an external pull-up on MCLR and
not use the internal.
I dunno why.
I could be wrong in my recollection - usually am.
Can anyone shed more light?

 

[john jardine]

"R.Lewis" <h.lewis@connect-2.co.uk> wrote in message
news:36v3l6F536atiU1@individual.net...

Interesting that bit about the internal MCLR being 'dodgey'.
Could you explain further?

regards,


There's no problem with the internal MCLR action . It's just that when it's

programmed 'out' then the PIC reset action falls back to a second (less
secure)level, of being reliant on the internal power-on-timer.
For this timer circuitry to do it's job it can only assume the PIC power
supply is OK. If the PIC supply is still thrashing about while the timer
circuitry is trying to count, then counting problems turn up.
It's one of those "who guards the guardians" type hardware conundrums that
the Microchip software people can't seem to grasp.
regrads
john