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PICList Thread
'Semi random reset'
1998\03\10@131411 by Javier Puiggros Vogel

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I have a pic16c74A connected to 4 PCB relays (5V) to open valves for humidity control, but sometimes the program reset and start again. The reset happen when the solenoid valves turn off. I tried using some caps in mclr and vdd pins but the problem don´t go.
I don´t know if there is an special values for the caps, or another solution than putting caps in the pins processor
some help?
 
javier Puiggros
vgr@interaccess.cl

1998\03\10@150905 by Andrew Warren

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Javier Puiggros Vogel <spam_OUTvgrTakeThisOuTspaminteraccess.cl> wrote:

> I have a pic16c74A connected to 4 PCB relays (5V) to open valves for
> humidity control, but sometimes the program reset and start again.
> The reset happen when the solenoid valves turn off. I tried using
> some caps in mclr and vdd pins but the problem don't go. I don't
> know if there is an special values for the caps, or another solution
> than putting caps in the pins processor some help?

Javier:

Do you have diodes across your relays?

-Andy

=== Andrew Warren - .....fastfwdKILLspamspam@spam@ix.netcom.com
=== Fast Forward Engineering - Vista, California
=== http://www.geocities.com/SiliconValley/2499

1998\03\10@194210 by Eric H

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You have to look at the transients of your power supply.  If you do not have
a seperate power source for your controls, and the valves, you will get
spikes on your power.  One way is to use opto-couplers between the dirty
power on the valves, and the control power.  We built robotic controllers,
and had problems with static RAMS that would erase because of pneumatic
valves.  Finally went to EPROMs, and that cleared up the problem.  Huge EMF
surges occur when a valve opens.  Clamping diodes help, but you still get
surges on the line.

{Original Message removed}

1998\03\10@224301 by Mike Keitz

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On Tue, 10 Mar 1998 14:55:27 -0400 Javier Puiggros Vogel
<vgrspamKILLspaminteraccess.cl> writes:

>I have a pic16c74A connected to 4 PCB relays (5V) to open valves for =
>humidity control, but sometimes the program reset and start again. The
>=
>reset happen when the solenoid valves turn off.

Both the relays and solenoid valves, being inductive, will generate a
surge of voltage when turned off.  Connecting any heavily inductive or
capacitive load directly to a PIC pin is likely to cause trouble.  Don't
expect the protection diodes in the PIC to carry heavy current and still
maintain proper operation.  They are intended mostly to prevent permanent
damage.  Use an external diode arrangement to prevent any voltage higher
than Vdd from reaching the PIC.  The best way to do it is to use driver
transistors for each relay.  The base resistors will isolate the PIC
fairly well.  It may be possible to drive the solenoids directly from the
transistors without using relays.  The relay power should be drawn from a
source other than Vdd (such as the raw input to the regulator).  In any
case, the relays or solenoids need to have diodes to shunt out any
inductive "kickback".

Dumping the inductive kickback into the Vdd line can also cause trouble.
If the circuit doesn't use a lot of power, the burst of energy from a
relay coil can make Vdd jump well above 5V.  A large capacitor (1000 uF)
from Vdd to ground can limit this voltage rise.  Such a capacitor should
be standard in any design that's used in a noisy environment anyway.

If driving the solenoids via relays, the inductive "kickback" from the
solenoids can make the relay contacts arc as they open.  The
high-frequency energy from this arcing may couple into the PIC and
disrupt it.  It also is likely to shorten the life of the relay.  Either
an MOV or a series resistor-capacitor snubbing network can be connected
across the solenoid coil or maybe the relay contacts to reduce this
problem.  Just using a capacitor would make the relay contacts arc as
they close.

If you still have problems, test without the solenoids connected or
energized to see if it's coming from the relay coils or the solenoid
coils.

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1998\03\11@085250 by VGR

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>Both the relays and solenoid valves, being inductive, will generate a
>surge of voltage when turned off.  Connecting any heavily inductive or
>capacitive load directly to a PIC pin is likely to cause trouble.  Don't
>expect the protection diodes in the PIC to carry heavy current and still
>maintain proper operation.  They are intended mostly to prevent permanent
>damage.  Use an external diode arrangement to prevent any voltage higher
>than Vdd from reaching the PIC.  The best way to do it is to use driver
>transistors for each relay.

I have transistor drivers for each relay and also have diodes in the coil of
the relay.

>Dumping the inductive kickback into the Vdd line can also cause trouble.
>If the circuit doesn't use a lot of power, the burst of energy from a
>relay coil can make Vdd jump well above 5V.  A large capacitor (1000 uF)
>from Vdd to ground can limit this voltage rise.  Such a capacitor should
>be standard in any design that's used in a noisy environment anyway.

Also  I have large cap in the power supply (+-1000 uF)

>If driving the solenoids via relays, the inductive "kickback" from the
>solenoids can make the relay contacts arc as they open.  The
>high-frequency energy from this arcing may couple into the PIC and
>disrupt it.  It also is likely to shorten the life of the relay.  Either
>an MOV or a series resistor-capacitor snubbing network can be connected
>across the solenoid coil or maybe the relay contacts to reduce this
>problem.  Just using a capacitor would make the relay contacts arc as
>they close.

I'll probe with the snubber (100 Ohm and .1 uF I think)

>If you still have problems, test without the solenoids connected or
>energized to see if it's coming from the relay coils or the solenoid
>coils.

The circuit has no problems without load. When I connect the solenoid I get
the reset
I still don't know if a power on reset or an mclr reset is the signal that
reset the circuit

thanks for the suggestion I'll probe it

1998\03\11@132746 by Tom Handley

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  Javier, without knowing the details of your project I would recommend:

1. Use MOSFETs instead of relays.

2. If you have to use relays, use MOSFET or bipolar buffers. Use a separate
power supply for the relays. Make sure you have diodes across the relay
coils to suppress voltage spikes. Consider an R-C `snubber' network across
the relay contacts. The values of R and C vary depending on the
characteristics of the valve solenoids.

3. If the solenoids use 5V, use the relay supply or a separate supply if
you switch to MOSFETs.

4. Route the relay/MOSFET/etc and solenoid grounds to a common source that
supplies the PIC and solenoid power.

  If you can provide more details about the valve solenoids such as voltage
and coil resistance, I'm sure many folks here can provide more help.

  - Tom

At 02:55 PM 3/10/98 -0400, javier Puiggros wrote:
>I have a pic16c74A connected to 4 PCB relays (5V) to open valves for
>humidity control, but sometimes the program reset and start again. The
>reset happen when the solenoid valves turn off. I tried using some caps in
>mclr and vdd pins but the problem don«t go. I don«t know if there is an
>special values for the caps, or another solution than putting caps in the
>pins processor some help?
>
>javier Puiggros
>.....vgrKILLspamspam.....interaccess.cl

1998\03\11@202630 by VGR

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I probed today the RC snubber but its appear to get better  but not safe of
reset. I will explain a little more my project:

I'm using 24 VAC solenoid to open water valves, far about 5 to 10 meters
The solenoid is 1,7 Va (app 123 ma AC) and has 36 Ohm.
The relay is connected to the same power supply that the PIC. They are 5 VDC
relays and support 0.5 A. I put the relays in other PCB with the npn
buffers.
The trafo that supply the Pic is the same that I supply the solenoid (may be
the problem?)
I'm using 100 nF between the Vdd and Vss.
The power supply is with a LM7805
I don't know if is a mclr reset or a power on reset but it appears to be the
second, because some times the Pic goes on and don't return.

thanks for the help, and hope this information can help.

PD some times I get duplicated mail???

Javier
EraseMEvgrspam_OUTspamTakeThisOuTinteracces.cl

1998\03\11@235636 by tjaart

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VGR wrote:

> I probed today the RC snubber but its appear to get better  but not safe of
> reset. I will explain a little more my project:
>
> I'm using 24 VAC solenoid to open water valves, far about 5 to 10 meters

And inductive load over 10m is sure to confuse your PIC.

> The solenoid is 1,7 Va (app 123 ma AC) and has 36 Ohm.
> The relay is connected to the same power supply that the PIC. They are 5 VDC
> relays and support 0.5 A. I put the relays in other PCB with the npn
> buffers.
> The trafo that supply the Pic is the same that I supply the solenoid (may be
> the problem?)
> I'm using 100 nF between the Vdd and Vss.

This will only help if it is right next to Vdd & Vss.

> The power supply is with a LM7805

Use 100uF cap with a flyback diode after the regulator. Put an in-line
10ohmresistor in the Vdd line after that followed with a 10uF and a 100nF.

Be sure that your MCLR line is hooked to the clean power.

> I don't know if is a mclr reset or a power on reset but it appears to be the
> second, because some times the Pic goes on and don't return.
>
> thanks for the help, and hope this information can help.
>
> PD some times I get duplicated mail???

Us geeks geeks tend to tend to repeat repeat ourselves ourselves.

--
Friendly Regards

Tjaart van der Walt
tjaartspamspam_OUTwasp.co.za
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