robotmaker
Started this post on how to add more digital and analog ports to your EZB without losing speed or spending over $70 for another EZB
EDIT 3-31 ITS $69 FOR EZB and to usa its $25.56 CHEAPEST rate without tracking to other countries its a lot more. BOARD COST for circuit is under $3
BUT in my post there is disadvantage and advantages of both ideas ,EZB and multiplexer circuit
PART ONE ANALOG MULTIPLEXING
Analog multiplexing is using only one ADC port and have more then 16 analog inputs and depending on analog ports needed will depend on how many digital ports are used to switch it
VERY simple circuit only one chip under $1 will post a schematic up in a day or 2 and part # of the chip
Its analog switch so it very fast ,not much coding is needed ,not like using 2 EZB and have to pass info back and forth using bluetooth or USB or wifi
Analog ports the EZB only has a few,and needed for analog sensors or other boards like battery monitor ,or current on digital there is more then twice as much
PART 2 will be digital multiplexing PART 3 will be using I2C bus
I love your disclaimer!
MAIN problem most overlook is the speed of the bluetooth ,compare to speed of digital chip witch is less the microseconds.
You see that first you need to send info to the second board and then to port you want to use and then receive the info back using bluetooth again.
NOW using a digital chip you dont have that problem ,but there may be limitations ,just like in USING 2 EZB'S ,havent tried it or anyone else tried it too
Like the getping WILL NEED TO TRY IT,might be a easy fix for it.
I guess best way is the testing of it.
BUT check the speed of the bluetooth communication and compare to digital.
ANOTHER item others dont look at is size of the EZB and extra current it needs.
Adding the board is just like adding another sensor or using the serial command to another board
I see mostly nobody really try it (like me)so its kinda hard to say it may or may not have problems.
Its not made for every sensor or digital add-ons ,but it does help.
ONCE i build it witch takes less the hour only a few pins to solder will test for different add-ons
PLUS there are same chips that uses 4 output with one in,and 8 out 1 in ,so it uses less control lines to control it.
A (very) quick Example Project for testing the circuit.
Imagine the circuit built, two servos connected to sub ports 0 and 1 (or 1 and 2 depending on how you name them)
D0-D3 are the control ports. D4 is the passthrough. Two servos, set to D4. Two scripts, one which sets servo on sub port 0 to a low position randomly the other that sets the other servo to a high position randomly.
Run each at different times and you have no problems. Run both together and there will be times when the low position servo hits a high position and vice versa. The control portions of each script fight each other for control of the digital ports. ARC does not know the servo positions for the two servos and believes both to be the same.
This is with only two devices. Imagine the confusion and problems with having 16 devices on one port.
A major problem if limits are set on one servo and another pushes it past those limits, possibly causing physical damage.
This is just one limitation I mentioned.
One does not need to build the circuit in order to know the outcome. multiplextest.EZB
And again, this is for the benefit of those who are deciding on which method to use. This is not an argument against any design and as such is not open for debate. Users may use this post as they see fit and are free to disregard it should they wish to. All datasheets and documentation has been digested prior to this posting.
Please, build the circuit. Test the circuit thoroughly. The limitations mentioned will be there, I personally guarantee it.
Wow, will you two ever both just agree on a statement?
I have a large project with lots of things going on and a few constantly running scripts. I've ran my robot on both 2 boards and now 3. One of the boards is fully loaded with Digital and ADC ports filled. The other two are less then 1/4 filled. At first when I started using 3 boards I had an issue with one or two Bluetooth connections disconnecting. Also I had bad lag problems with all my scripts running variables and monitoring ADC ports. The internal Bluetooth on my older laptop running Win 7 couldn't handle the extra load and it was a bottleneck. Following DJ's advice I disabled the internal Bluetooth and started using a USB 3.0 Bluetooth Dongle in one of the laptops 2.0 USB ports. That solved my connection and lag problems using 3 boards.
Never had slowdown or connection problem with using just two boards connected to the laptop with the old internal Bluetooth set up. And I had a lot going on in ARC.
However last night I tried to use a different "2.0" USB Dongle in place of the 3.0 Dongle. I started having the same old issues till I put the 3.0 back in. Also had the same results on a different Laptop from the same era. So, there is a speed issue with Bluetooth and Dongles are all not created equal. I have a feeling it's the way the Dongle is made and how good it's antenna is.
With all that said it still seems that the better choice would be to get a second (or third) EZB Board and to avoid the many other pitfalls described using Robotmakers idea. To avoid the Bluetooth bottleneck one could convert EZB to Wifi or USB. Still Robotmakers board would be an interesting experiment to try.
Early on DJ himself suggested to me in another post to "get inventive" and try to come up with a way to multiplex an ADC port to make two connections to it. Someone suggested using a simple resistor. I'm not knowable enough to do this but (personality aside) I'm glad it's being discussed and tried. 
Thanks DAVID,but kinda hard to tell if the EZB is faster then using a straight digital board
IT seems i qam always wrong with RICH ,but its not a problem
Testing the board is the best way.
ON multiplexing analog ports there are many ways to do it with out using resistors.
KINDA hard to read one vaule with 2 resistors sending the same data at the same time,how does it know witch resistor has the data without a switch
on multiplex chip it is like spdt switch,now you can use 4066 witch is a single switch .