More 12v outputs?

[skipmcnoob@yahoo.com]

Hello all!
does anyone know of a possible way to set up the prop2 for more 12v outputs? possibly exchanging the 2803 out for another IC? I have a valve bank that is 12v that i need to power with the prop2.

Thanks

[JackMan]

How many valves do you need to control?

[skipmcnoob@yahoo.com]

8 currently. maybe more later...

[bsnut]

The Prop-2 is designed to provide you with only 16 I/O pins This I/O is also connected directly to the ULN's. So, if you want extra outputs you may want consider the HC-8+, which uses 1 I/O pin and communicates serially. The HC-8+ has 8 transistors to provide you what you need. The cool thing is it also provides you with 8 inputs.

[skipmcnoob@yahoo.com]

I think there might be a miss understanding, a fault of my own of corse. Im not looking for more outputs, from what i understand the prop2 only has 6 outputs that output 12v. Is there a different ULN that i can plug in that makes ALL of the outputs 12v instead of six of them 12v and nine of them 24v which the board is currently configured to be?

BTW, Thanks for all the help! You guys rock!

[bsnut]

I think you are a little confuse about the Prop-2, but that's ok :).

The Prop-2 is based on the Basic Stamp 2 processor by Parallax. This processor has 16 I/O (input/output) pins that can be input or output and each are connected to the servo header and the input side of ULN. This means 8 I/O pins of these pins are connected to one ULN and the other 8 I/O pins are connected to the other ULN.

The ULN is a transistor array, which is able to handle 12VDC or 24VDC at the OUTx terminals. The voltage at the OUTx terminal is base on the voltage of the power supply plugged (12VDC or 24VDC) into the Prop-2 and when you set the power switch in position 2, it places the power supply voltage on the screw terminal "V+".

So, in order to operate a 12VDC solenoid you will have one wire of the solenoid connected to "V+" and the other wire of the solenoid connected to one of OUTx terminals and the power switch set to position 2.

Here is a link to a topic that Jon started, that talks a little about the Prop-2 and it also goes into detail on the setup jumpers used on the Prop-2 as well. 
http://www.efx-tek.com/php/smf/index.php?topic=6.0
Also, here's the link to the PDF on the Prop-2 as well.
http://www.efx-tek.com/downloads/prop-2_docs.pdf

[JonnyMac]

Technically you could have all 16 Prop-2 outputs on at the same time.  The issue is not voltage, but current.  The ULN2803 only allows so much current and if you exceed that it can overheat and burn up. 

We put a chart here:
-- http://www.efx-tek.com/php/smf/index.php?topic=567.0

As you can see, with eight outputs on at the same time you need to limit the current to them to about 170mA (~2W).

[skipmcnoob@yahoo.com]

By God I think I've got it :P
Thank you guys for all the help and links!
I was not aware that the output voltage was based on the input voltage, but it does make perfect sense. May I ask what the 2803 is for?

[JonnyMac]

May I ask what the 2803 is for?

It allows the small microcontroller on the board (BASIC Stamp 2) to switch higher voltage, higher current loads.  Think of it as a package simple solid state relays.  Inside are eight Darlington transistors and some protection diodes.  Darlingtons allow you to use a tiny current to swtich a much larger one.

[skipmcnoob@yahoo.com]

Ohh okay. So the 2803 is powered with 24v and you can use a 3v signal to trip the relay? Sorry for all the questions it just helps me understan the board better, and its super interesting!  :P

[JonnyMac]

Actually, no -- I probably should have done a better job with the SSR explanation. 

Think of the ULN as a normally-open switch connected to ground.  When the circuit is active the ULN provides the ground side of the power supply to your device.  This is why the Prop-1 and Prop-2 have a "hot common" (V+ terminal): the ULN is switching the ground side.  You can even use an offboard DC power supply to your valves/relays, so long as the ground from that power supply is connected to GND on the board.  We don't recommend this, however, as that bypasses protection diodes inside the ULN.