Dual Hi/Low Relay CK1619 from Carl's Electronigc

[kenqu]

hello, 

First time poster.  I have read the forums on relays and have not found anything about the type of relay I am using.  It is a "dual hi/low relay kit (kit ck1619) from Carl's electronics.  According to the documentation it can be triggered by either a high or low input.  On the board there are terminals for V+, Ground, High, Low.  I am using the prop-1.  I have the V+ out from the prop -1 connected to the V+ on the relay board, the Ground out from the prop-1 connected to the ground of the relay board, and the Out3 connected to the High input on the relay board.  when I do this, and test the voltage I see 12 vdc across the V+, and the high as well as v+ and ground.  I have included a selection from the kit manual:

How it Works. The kit is based around the ULN2003A
IC, a 7-channel high voltage, high current relay driver.
The inputs are TTL compatible, allowing them to be
directly connected to logic circuits operating from a
supply voltage of 5V.
Each driver is effectively a logic inverter with an open
collector output, meaning the 'load' is connected between
the output pin and V+.
Looking at the schematic we see that there are two
identical circuits, one for each relay. Operation is the
same for both so we will refer to the RL1 circuit only in
the following explanation.
There are two inputs that can be used to operate the relay,
marked LO and HI. As the names suggest a low on the
LO input will operate the relay. Similarly a high on the HI
input will also operate the relay.
The LO input operates the relay via IC1:A and IC1:B. A
low level input will be inverted by IC1:A and its output
will be high. Then this high is inverted again by IC1:B to
give a low output to operate the relay. Resistor R1 holds
the input high when not used.
Now 'hang on' you might say – why invert a low to a
high then just invert it low again? Why not connect the
LO input direct to the relay and forget about using IC1:A
and IC1:B? Good question. The answer is that if you
connect the LO direct to the relay you lose all control
about what voltage the LO input can be. An input of 3V
for example, will trigger the relay closed. This will
probably be quite undesired. By using the two relay
drivers to process the signal the LO must be no more than
0.8V. Anything over that will not trip the relay and you
have full control.
The relay can also be operated via the single inverter
IC1:C. In this case a high level on the HI input is inverted
by IC1:C and the resulting low output will operate the
relay. Resistor R3 holds the input low when it is not used.
So, the relay will be operated when either the LO input is
low (0 – 0.8V) or the HI input is high (2.4V – 12V.).
Note that the outputs of IC1:B and IC1:C are connected
together. At first glance it might seem that they would
destroy each other if one was high and the other low. This
cannot happen because the outputs are 'open collector',
meaning that the inverter can drive the output low but it
relies on an external device to pull the output high. In this
case the external device is the relay.
Tying open collector outputs together like this is known
as a "wire OR' configuration. It means that the relay is
operated when either the IC1:B output OR IC1:C output
is low.
Diode D1 provides reverse polarity protection in case the
power supply to the kit is connected the wrong way
around.

I have attached the complete manual

I guess my question would be, can I use this relay board with the prop-1, if so how should I make the connections?  And how should I trigger it.

[kenqu]

OK, I figured it out.  I am using the code John wrote to activate the Cowlacious board.  After reading through the code I noticed he was pulling the out5 low.  I changed the connections from the prop-1 to the relay board by connecting out5 on the prop-1 to the low input on the relay board.  Everything now works great.  BTW if you don't mind a little assembly these relay boards are great.  It takes me about 30 min to assemble one.

[BigRez]

BTW if you don't mind a little assembly these relay boards are great.  It takes me about 30 min to assemble one.

I've found similar boards available on eBay and they're already assembled.  I've purchased several (2- and 4-relay boards) and they are really nice little boards.  Plus, the cost (inc. shipping) is less than the kit you mention.  To see them, search for "2 relay board 12v" on ebay.

[JonnyMac]

Your best bet would be to use an OUTx single into the LO inputs -- this is going to be the safest connection.

[kenqu]

That is the connection I finally came up with.  Not sure why it works, but hey I'm not going to argue with success.

Thanks

[JonnyMac]

It works because you're going through two-stages of inversion -- low in means low (ground) to the side of the relay coil that needs ground.  The inverters used are open-collector so either one of the inverters connected to the coil can make it activate.  It's best to go through the ULN as that serves as a buffer between the boards. 

You *could* connect a Px output to the HI input pin but I don't recommend this; if the inverter on the other board fails you could get 12v directly into the processor and break it.