NEWBIE, Needs info for additional A to D inputs.

Frankfern123

Hi All, today's stupid question is as follows.............

I'm using the Prop BOE as my test base and I need more ANALOG inputs. From what i can gather the Prop BOE can only handle one at a time, maybe two. I need to source 8 separate voltage signals ranging from 0-5 VDC including one that reads -5 - 0 +5 for a differential circuit.

Parts, schematics and source code links would be greatly appreciated.

ALSO OPINION NEEDED - Being I'm so new to this as a whole, would I be better off switching over too the new C language based Prop. It seams to me it will be easier to learn.


Thank you all in advance .......................

Publison

Frankfern123 wrote: »

Hi All, today's stupid question is as follows.............

I'm using the Prop BOE as my test base and I need more ANALOG inputs. From what i can gather the Prop BOE can only handle one at a time, maybe two. I need to source 8 separate voltage signals ranging from 0-5 VDC including one that reads -5 - 0 +5 for a differential circuit.

Parts, schematics and source code links would be greatly appreciated.

ALSO OPINION NEEDED - Being I'm so new to this as a whole, would I be better off switching over too the new C language based Prop. It seams to me it will be easier to learn.


Thank you all in advance .......................

The A/D on the Prop BOE will handle 4 analog inputs, (at the same time). You could add another that does another 4 to the available lines, or the I2C buss that the original A/D is on, but with a different address.

There is no "C" based Prop. C programing has been available for a number of years, along with SPIN and PASM on the Prop 1.

Mike Green

The Prop BOE's ADC (Analog to Digital Converter) is designed for 0-5V inputs. If you need some other voltage range, you can transform that to 0-5V using an op-amp buffer designed for that. Usually for a -5V to +5V input, you'd need an op-amp operating from both +5V and -5V supplies, so you'd need an additional power supply for the -5V.

As Publison mentioned, you can add another ADC of the same type using the same circuit for an additional 4 analog lines (with a different I2C address ... set when you wire up the ADC AS pin).

Other programming languages available include several versions of Forth and Basic.

Frankfern123

Thanks for the info, do you know where i can find some more documentaion on how to wire it up properly. The learning System does not seam to explain it at all or I'm clearly missing something.

Aslo about programming in "C" - This is what I was referencing - http://learn.parallax.com/propellerc

Mike Green

"wire it up properly" - define properly. The Prop BOE is already wired for lots of things. If you want to use the VGA display feature, you have to add some jumpers. If you want to use the xBee socket, you have to add some jumpers. These are done this way because the features use a lot of I/O pins and Parallax didn't want to reduce the available I/O pins below 16. The audio and video outputs are wired. The ADC and DAC connections are wired. The micro-SD card connections are wired.

The link you showed is indeed the starting point for Propeller C programming. The exercises are mostly intended for the Propeller Activity Board, but the Propeller BOE is essentially an extended version of that. Have a look at the documentation for each board and you'll see how they relate to each other.

Publison

There are links in the bottom right of the product page, and one specifically, http://learn.parallax.com/PropellerBOE . Follow the link to "Measure Voltage"

Frankfern123

Mike Green wrote: »

"wire it up properly" - define properly. The Prop BOE is already wired for lots of things. If you want to use the VGA display feature, you have to add some jumpers. If you want to use the xBee socket, you have to add some jumpers. These are done this way because the features use a lot of I/O pins and Parallax didn't want to reduce the available I/O pins below 16. The audio and video outputs are wired. The ADC and DAC connections are wired. The micro-SD card connections are wired.

The link you showed is indeed the starting point for Propeller C programming. The exercises are mostly intended for the Propeller Activity Board, but the Propeller BOE is essentially an extended version of that. Have a look at the documentation for each board and you'll see how they relate to each other.

Ok gotcha on that, but I'm still confused about how to wire up 4 devices on the board. The lesson in "Prop learn" uses 3 out of the 4 pins. 1 for 3.3VDC, 1 for GROUND and 1 for the device VOLTAGE signal.

Do i have to use 2 out of the 4 ADC pins for 3.3V and GRD or can I use all 4 ADC pins for the return signal and source the #># and GRD elsewhere in the circuit?

Thank you ..........

Publison

Could you reference the exact link? The VDD and Ground are already connected to the chip.

EDIT: I don't actually own a Prop BOE, but by the schematics, you have four inputs in the lower right AD 0-3. Your analog input would go there, referenced to the ground pins to the left, (GND).

Frankfern123

Publison wrote: »

Could you reference the exact link? The VDD and Ground are already connected to the chip.

EDIT: I don't actually own a Prop BOE, but by the schematics, you have four inputs in the lower right AD 0-3. Your analog input would go there, referenced to the ground pins to the left, (GND).

This is what keeps confusing me .............http://learn.parallax.com/node/113

Publison

I agree, it may be quit confusing. The connection to AD0 is the only one measuring changing voltages from the pot. the other two connections, (GND and 3.3V) , just show that you can monitor another two voltages at the same time.You can pull out the AD1 and AD2 wire, and monitor your other voltages. Of course you have to provide the ground connection for each of them.

BTW, the docs say there are three sockets labeled AD0, AD1, and AD2. There is a fourth, AD3. I need to send that little tidbit of info the Parallax.

Mike Green

The example given on the Learn webpage is just that, an example showing the measurement of +5V, 0V, and a 3rd voltage set by a pot acting as a voltage divider between +5V and 0V (ground). You can use any of the ADC inputs (AD0, AD1, AD2, and AD3) to measure voltages between +5V and 0V.

Frankfern123

Awesome, Thanks guy's. This is what I suspected but was afraid to fry my board in experimenting around with it.

I appreciate your patience and help .............