hacking the demo board

nisbus

Hi,

I have a demo board (#32100) and while it was a good start to get familiar with the propeller I'm a little annoyed with having 8 useless leds on it and only 8 inputs.
I really need 16 inputs and was wondering if I could remove/bypass the leds and turn pins 16-23 into inputs.

My electronics experience is very limited as is my knowledge of electricity in general.
I know how to solder but that's about it.

Can someone please help me with getting the leds to pass as inputs since I really don't want to spend another $50 for a new board with more inputs?

thanks,
nisbus

obrienm

nisbus,
Welcome, why don't you try getting a protoboard or protoboard USB unless you need the demo board specific connectors. I can solder headers on a protoboard fine - but the surface mount LED's on the demo board - I don't know I try to stay away from microscopic non 0.1 work? I think you will need some steady fingers and some drilling (don't know if the board is 2 or 4 layers). Worst case you could multiplex the inputs with a 165 or 597 into 3 pins and take the PISO bits back into 16 on the propeller (like the reverse of a SIPO 595 output expansion). Theoretically the propeller can do any number of inputs or outputs with 3 pins and 165/595's or full-duplex shared I/O with 4 pins (one pin to control a in/out tranceiver chip like the 641/643 - there are only 4 user pins on both the oledProp and the Spinneret for example) - of course the "multiplexing" pattern negates the parallel nature of the propeller - in that one cog must perform I/O and feed the other 7. Just one of 10's of ways probably possible.

More on 165 parallel-in serial out multiplexing:
I have a project where I need to read 8 outputs from 80 propeller chips into a single host propeller - that is exactly like your problem of 16 inputs - instead I have 640. Instead of having 640 lines running into the host propeller I put a 165 chip next to each propeller chip that reads in the 8 lines for that chip. I daisy chain the 80 165 chips as long serial line of 640 bits (with proper fanout buffers every 8 chips). The spin code just does a shift in on the "single" data line 640 times - yes, not very fast or parallel but it saves a lot of input lines.

Note: due to a 5A max I have only tested this up to 16x8 lines so far (not using an OBEX 165 driver - but driving the data input and shift lines using plain outa spin commands).

Just thought of another design: You could use a data selector like a 151/251 - you would need 2 of them. You feed the 16 inputs into the 2 - 8 bit data selectors and get 2 bits at a time (one for each set of 8).

Parallax sells the 165 chip, you should be able to get the 151 and the datasheets from digikey or future.

The propeller works very well with any 74HC family chip.
thank you
Michael O'Brien

potatohead

I would second that.

Having a demo board available is a good thing. Lots of code runs on it, and it's a great sanity check for other projects.

Proto boards are great for what you describe.

nisbus

Thanks for the replies,

I was afraid that would be the conclusion (although I only understood about a fifth of what you wrote )

I guess I'll have to invest in the USB board.

thanks,
nisbus

hover1

nisbus wrote: »

Hi,

I have a demo board (#32100) and while it was a good start to get familiar with the propeller I'm a little annoyed with having 8 useless leds on it and only 8 inputs.
I really need 16 inputs and was wondering if I could remove/bypass the leds and turn pins 16-23 into inputs.

My electronics experience is very limited as is my knowledge of electricity in general.
I know how to solder but that's about it.

Can someone please help me with getting the leds to pass as inputs since I really don't want to spend another $50 for a new board with more inputs?

thanks,
nisbus

To hack the Demo board in a way you are considering would require de-soldering the 8 LEDs. Then removing the 8 SMD resistors to the VGA circuit, and replacing them with wire across the pads. You would then have access to P16-P23, through the VGA connector, but you will have given up the VGA output of the Demo Board.

Perhaps you didn't take a look at the Propeller Professional Development Board

It's actually on sale now and will provide all 32 I/O's plus all the connections a Demo board will do. Completely reconfigurable.

The ProtoBoard is also a bargain. Solder a few female connectors as others have said, and it another type of demo board.

I guess it all depends on the funds.

Jim

mwalimu

On the demo board you have 4 pins available from the mouse and keyboard ports with no modifications. There are also two pins on the VGA port that (vga14 & 13 -p16 & 17). If you decide you don't need the VGA port, you can remove one of the resistors that make the RGB network. There are three uncommitted pins on the VGA plug and you can solder a small bit of wire from the those lines to the VGA socket.

Check the Demo Schematics for details.

Humanoido

The Demo board is a great investment and very versatile. In a recent project, I used a Parallax Demo Board and simply reclaimed a number of pins. In my project, I wanted more pins for LEDs. You can use these pins for your own purpose. Consult the schematic for working through the resistors on board. You can push a spring connector, wire or plug into the TV jack and gain a fast pin for a quick circuit.

How to Reclaim Pins for LEDs (Demo Board)
P0 - P7 Main Header = 8 pins (Vss)
P16 - P23 LEDs on Board = 8 pins (Vss)
P12 - P15 TV = 4 pins (Vss)
P24 - P25 Mouse = 2 pins (Vdd)
P26-P27 Keyboard = 2 pins (Vdd)
P29 EEPROM = 1 pin (after booting, Vdd)

---

total 25 pins

prof_braino

What the others said.

Don't kill your demo board, you'll want it intact when you get past the point your at now.

For your skill level, ideally you really want the professional development board. AND you want to do all the examples in the manual.

You wouldn't want to do the proto board yet unless you want to subject yourself to a crash course in electronics. In my case, I got 1) demo board, 2) proto board, 3) Pro Dev board. Looking back, I should have gotten Pro Dev board first. The protoboard is for when you want to commit a tested and proven design to solder. Possible for a beginner, though more suited for experienced. I still use the demoboard often, it almost always works with OBEX examples, its handy to have a standard reference.

Cluso99

@nisbus: Please tell us what sort of inputs you require (what are you inputting)? What connections are you already using? Then we can point you in the right direction.

The DemoBoard is a good board for beginners, but of course will not do everything you may want.

So, hopefully there will be no reason for you to buy another board yet. There are a number of pins available which can be used as inputs depending on what you are actually wanting to connect.

nisbus

I'm want to input 10 buttons and a tri-axis accelerometer to the demo board.
I'm building a keyboard that has 10 buttons and using the accelerometer as a mouse input.
I'm currently using all the inputs available 0-7 (three for the accelerometer and then 5 for buttons).

I don't really want to destroy the demo board as far as PS/2, composite, audio inputs/outputs but I wouldn't mind getting rid of the leds. It makes no sense to me to use 8 pins for leds on a board like this. They should be additional input/outputs since plugging a led to a bread board is probably the simplest thing you can do.
I realize from earlier responses that messing with the leds on the demo board is hard work due to their small size (my soldering skills don't cover soldering to such small objects.)

I will probably take prof_brainos advice and get my self the Pro dev board. It looks like a sound investment for future projects.

Thanks,
nisbus

prof_braino

nisbus wrote: »

It makes no sense to me to use 8 pins for leds on a board like this.

I will probably take prof_brainos advice and get my self the Pro dev board. It looks like a sound investment for future projects.

The 8 LEDS are on 16-23, which I think are also the VGA output.
http://www.parallax.com/dl/docs/prod/prop/PropDemoDschem.pdf

They (also) light up when the VGA is working correctly; they are an "extra", not an "instead of". I think that is the reasoning.

Sapieha

Hi nisbus.


You only need remove 3 resistors to have this pins usable for most of types of DIGITAL signals IN/OUT.

and LED's will not disturb them (only give You visual info what hapens on this pins)

BUT in that configuration ---> You can't use that pins as ANALOG input pins

nisbus wrote: »

I'm want to input 10 buttons and a tri-axis accelerometer to the demo board.
I'm building a keyboard that has 10 buttons and using the accelerometer as a mouse input.
I'm currently using all the inputs available 0-7 (three for the accelerometer and then 5 for buttons).

I don't really want to destroy the demo board as far as PS/2, composite, audio inputs/outputs but I wouldn't mind getting rid of the leds. It makes no sense to me to use 8 pins for leds on a board like this. They should be additional input/outputs since plugging a led to a bread board is probably the simplest thing you can do.
I realize from earlier responses that messing with the leds on the demo board is hard work due to their small size (my soldering skills don't cover soldering to such small objects.)

I will probably take prof_brainos advice and get my self the Pro dev board. It looks like a sound investment for future projects.

Thanks,
nisbus

CumQuaT

To be honest, I wouldn't use the propeller demo board at all, but instead get the professional development board, that way you get access to all of the pins as WELL as having handy things like the LEDs when you need them. It's not that much of a price jump above the demo board and gives you a much nicer setup to work with. I swear by mine!