Making continuity (as well as sensing continuity)

Comments & issues
joelmaxuel
Fresh meat
Posts: 3
Joined: Mon Jul 15, 2019 11:56 am
Contact:

Making continuity (as well as sensing continuity)

Postby joelmaxuel » Mon Jul 15, 2019 12:16 pm

Hi,

A while back I was gifted a couple InterfaceKits - an 8/8/8 and a 0/16/16 - the older models as they connect by standard USB B.

I apparently had some weird assumptions about the digital inputs and outputs. I am looking to (input side) check the state of a switch to see if it is open or closed (continuity). I would have code (to be written) that once that state is seen, do things including close a different circuit (make continuity) momentarily.

The example above can be simplified by a doorbell - there is a switch outdoors. When that is pressed, I want (in part) the former switch to activate.

Was a bit surprised about the continual 230 Ohm resistance the outputs provide. How can I salvage this project? Keep in mind what I wanted of the outputs is to momentarily close a connection (currently five of these, independent of each other) of circuits typically powered by CR2032's.

User avatar
mparadis
Site Admin
Posts: 626
Joined: Fri Oct 28, 2011 12:17 pm
Contact:

Re: Making continuity (as well as sensing continuity)

Postby mparadis » Mon Jul 15, 2019 1:10 pm

The first thing to make note of is that the digital inputs and outputs on your 8/8/8 behave differently than the ones on your 0/16/16.

The digital inputs on the 8/8/8 are active low, meaning they will be "true" when tied to a low voltage (usually ground). On the 0/16/16, they're active high (true at 5V).

The digital outputs on the 8/8/8 are simple DC outputs: false is 0V and true is 5V. The outputs on the 0/16/16 are Open collector, or as I like to call them, "switch-to-ground" outputs. They are an open circuit when false, and are connected to the ground on the 0/16/16 when true. This makes them useful for bridging the low side of a simple DC circuit.

So in your doorbell example, the button should work with either input. If the doorbell has two wires, connect one to the ground on your 8/8/8 and one to an input. For the 0/16/16, connect one to the 5V terminal and the other to an input.

For the bell or whatever the other switch is connected to, if it's powered by 5V DC you can connect it directly to a 8/8/8 output. If it's more than that, the 0/16/16 output can be used to switch the low side of the circuit with the existing power supply.

If this isn't clear, you can draw a diagram of what wires are in your system and we can reply with a diagram of how to hook it up.

joelmaxuel
Fresh meat
Posts: 3
Joined: Mon Jul 15, 2019 11:56 am
Contact:

Re: Making continuity (as well as sensing continuity)

Postby joelmaxuel » Mon Jul 15, 2019 4:27 pm

By the sounds of the reply, I would be better off placing my outputs on the 0/16/16.

The devices power themselves (just needed a Phidget to close the switches I had since desoldered and broken out to leads) - one is powered by 5V, that doorbell in question was powered by a tiny 12V battery.

So that 5V switch series seems straight-forward to move to the 0/16/16 and does not seem to be any issue there (upon activating it's power source earlier with the 8/8/8, all the switches were activated even with the host machine powered off). With the actual 12V doorbell, sounds like I will require something between those doorbell leads and the 0/16/16 (to protect that Phidget).

User avatar
mparadis
Site Admin
Posts: 626
Joined: Fri Oct 28, 2011 12:17 pm
Contact:

Re: Making continuity (as well as sensing continuity)

Postby mparadis » Mon Jul 15, 2019 4:57 pm

The digital outputs on the 0/16/16 are capable of switching circuits of up to 30V, so I don't see any problems switching 12V to the doorbell. Just connect the positive wire of the 12V to the positive terminal of the doorbell, connect the negative wire of the doorbell to one of the 0/16/16 outputs, and connect the negative wire of the 12V to the ground of the 0/16/16.

joelmaxuel
Fresh meat
Posts: 3
Joined: Mon Jul 15, 2019 11:56 am
Contact:

Re: Making continuity (as well as sensing continuity)

Postby joelmaxuel » Mon Jul 15, 2019 6:54 pm

I moved the leads. Doorbell is theoretically fine. However the other device (an old key fob) is still sending signals on power delivery (not yet known if it is a momentary on power delivery or if the switches are closed for the duration).

I attached a (blurry, unfortunately) photo of the fob, and of where the other end connects to the interface kit. The white wire is soldered to the fob that makes a common side for all four former button faces. Then blue, green, orange and brown populate the other side of each button face. On the kit, I used 3, 4, G, 5, 6 with the white wire in the middle.

To avoid any confusion, I disconnected the G, 7 pair (output to doorbell transmitter) and applied power to the fob again, no change. I also (in case there may have been a short that developed on the fob) disconnected the white wire from the Kit, and applied the 5V again (this time, silence from the other end). I added the white wire back to Gnd again, and have returned to the same problem. Also (to clarify), given the behaviour of the fob, with all wires attached and power applied, the noticed response is from the button corresponding with slot 6. Disconnect that wire, reapply, and then the response would be the correspond from slot 5 (and so on).

Measuring between 4 and G, I see a resistance of approx 100K. FWIW, the lines for 0, 1 and 2 to their own Gnd does not detect any resistance as of now (they are currently lines that leave the project box; do not connect to anything otherwise).

Not sure what I could try next.
Attachments
IMG_20190715_204758crop.jpg
Kit
IMG_20190715_210211crop.jpg
Fob


Return to “General”

Who is online

Users browsing this forum: No registered users and 2 guests