PIC relays control

[Pic_User]

Hi Dom,

As I see it:
<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1883&stc=1&d=118558263 1" />
You would need a 5V relay to drive it directly.
The PIC 25mA limit would drive 200 or more coil Ohms.
Not:
Mono-stable Relay, normal relay that stays energized while a voltage is on the coil.
But:
Magnetically Latching, or Mechanical Latching Relays
Bi-stable Relay, “Latching “, usually means a pulse turns it on, a second pulse turns it off.
Single Coil Latching (1 coil latching), usually means the second pulse goes to same connection.
A single PIC I/O could give a pulse to turn it on, then later a second pulse would turn it off.

Dual Coil Latching (2 coil latching), usually means a pulse on coil A turns it on, a pulse on coil B turns it off.
This would require 2 I/O pins for control.

Here is a hook-up if you want to use a 12V relay.
<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1884&stc=1&d=118558290 6" />

You could also use a SCR that would latch with an impulse from a PIC I/O pin. It would be more difficult to un-latch.
-Adam-

[flipper_md]

Bi-stable Relay, “Latching “, usually means a pulse turns it on, a second pulse turns it off.

I would really like a relay that behave like that!
If it exist and the PIC can run it, that's what I want !!
But the spec sheets aren't very descriptive in that manner...(attached Panason TN spec)

double coils latching relays ask for 40mAh, and need 2 pins...

About FET and other electronics switcher, i'm trying to avoid tehm because they draw some power just for operating.

About Diodes, let's say I want to protect the PIC from the relay, I would use a 5V Zener?, or I need to add a safety margin? 4.5V?

Lots of Amps in the coil effect of a relay?


Thanks for all added info, i'm slowly but surely getting somewhere! 8)

[Pic_User]

Hi Dom,

I would really like a relay that behave like that!
If it exist and the PIC can run it, that's what I want !!
But the spec sheets aren't very descriptive in that manner...(attached Panason TN spec)

double coils latching relays ask for 40mAh, and need 2 pins...

About FET and other electronics switcher, i'm trying to avoid tehm because they draw some power just for operating.

About Diodes, let's say I want to protect the PIC from the relay, I would use a 5V Zener?, or I need to add a safety margin? 4.5V?

Lots of Amps in the coil effect of a relay?


Thanks for all added info, i'm slowly but surely getting somewhere! 8)

from the data sheet:
Panasonic TN Relays
1 Coil latching
TN2-L-5 V
5V 20mA 250-Ohm coil

The TN2-L-5 V should work directly from standard (25mA) PIC I/O pins.

I gave incorrect / incomplete information about latching relays in a previous post.
A single coil latching relay changes state when the polarity on the coil is reversed.

+++++ Info +++++
Single coil latching relay
DC Power to coil transfers contacts.
Contacts maintain after coil power is removed.
To transfer contacts to original position, DC Power to the coil is reversed.
Contacts maintain after coil power is removed.
+++++
Coil suppression circuit:
Circuit to reduce the inductive switch off voltage peak of the relay coil (EMC protection)
The latching relay protection diode would have to allow either polarity.
<img src="http://www.picbasic.co.uk/forum/attachment.php?attachmentid=1889&stc=1&d=118567495 4" />
Then your PIC would Make I/O A high and I/O B low or I/O B high and I/O A low, to latch or unlatch the relay.

We should mention that using the transistor in place of the relay does not use very much battery power.
But, the PIC has to remain in control of the pin driving the transistor.
I would consider using a logic level CMOS power transistor.
-Adam-