View Full Version : 4x4 Keypad,I/O pins,Demo Board

07-22-2009, 05:35 PM
Assuming, as suggested in the notes , that you plug the 4x4 keypad directly into P0-P7, where would you plug in a device ( for instance an LED driver) that you want to send an output . Can you use VDD since it will only be either off or "High" or would you share one of the I/O pins and let the propeller sort it out?

Mike Green
07-22-2009, 07:51 PM
Your question doesn't make a lot of sense. Can you explain what you are trying to do?

Vdd (along with ground/Vss) is a power supply terminal.

Microcontrollers don't "sort it out". Their I/O pins can be in input mode where they sense the voltage connected to them and are treated as "high" or logic 1 if the voltage is above a threshold (often 1/2 the supply voltage) or "low" or logic 0 if the voltage is below the threshold. If you connect a voltage much above Vdd or much below Vss (like a negative voltage), you may damage or destroy the microcontroller.

The I/O pins can be in output mode where they are effectively connected to either the "high" supply voltage (Vdd) or the "low" supply voltage (Vss/ground). An I/O pin in output mode can provide some current (usually 20-30mA depending on the device). If you try to draw more than that current, you may damage the microcontroller.

07-23-2009, 03:52 AM
I know my questions probably don't make sense to someone who knows what they are doing. Electronics is a hobby/second career for me. I am a veterinarian trying to construct a healing device. I've made a prototype with Basic Stamp that does most of what I want but I am trying to get more sophisticated by using Propeller. What I am trying to achieve;
Power an array of LEDs
Power an electromagnet
Power an audible noise maker ( that produces a healing sound like a purr or cricket)
pulse the power to the LED and Magnet at specific frequencies - said frequency being input with a keypad and readable on an LCD display.
I talked with tech support today and realized I can not do what I want with the demo board ie use the Pins 0-7 for keypad input and still be able to use the pins for other things. Fortunately I have a keyboard to do experiments with and hopefully once I get the programming right will be able to order Propeller chips preprogrammed with the pins free to do what I want. Any suggestions on what object to use with the keyboard?

Mike Green
07-23-2009, 06:17 AM
There's a keyboard object that comes with the Propeller Tool and interfaces to a standard PS/2 keyboard. There's also a variant called "comboKeyboard" in the Object Exchange that is compatible with the standard keyboard driver and a slightly different one used with the Hydra (since that has a little different hardware interface).

There are also objects for use with an LCD display and a keypad. Browse the Object Exchange (obex.parallax.com/ (http://obex.parallax.com/)).

There are several objects for driving LED arrays using various driver chips like the MAX6956.

There's an object for playing a WAV file of a sound. This would be better than trying to find a noise maker for something like a purr or cricket.

You can easily connect an I2C I/O expander like the Microchip MCP23017 that would provide another 16 bits of I/O and only need 2 Propeller I/O pins. There are other similar 8 bit I/O expanders by Microchip and NXP.

The Propeller doesn't come programmed (other than the bootloader and some tables and fonts which are in masked ROM). The user program gets written to an attached 32K or larger EEPROM by the Propeller under control of the Propeller Tool or other similar software on your PC. There's a write protect pin on the standard EEPROMs that can be wired to prevent the contents from being changed once loaded.

07-23-2009, 07:28 AM
Wow, that's a lot of great information - I really appreciate it.
(When I say programmed - the guys at Parallax mentioned that they could preload objects for me once they were determined)

07-23-2009, 11:33 AM
Hi Rich,

I would suggest instead of a keypad, to use a table of helpful frequencies instead because there are some harmful ones. A few buttons for up, down, enter should suffice then.
I would also suggest a protoboard. If you are using a LCD screen, you probably don't need the TV or VGA out. The amplifier built on the demoboard is kind of nice though, but can be done on the protoboard as well.
Is this a rife type healing machine? I am interested in doing this kind of stuff also. There is a guy (Glenn_Webber) that made a device on an SX. at http://forums.parallax.com/forums/default.aspx?f=21&m=362625.
There is also a Square Wave lab for the PE Kit here: http://forums.parallax.com/forums/default.aspx?f=25&m=343747.

I hope that helps.

Take Care,

07-23-2009, 06:43 PM
Hi Doug,
I am familiar with Rife in principal but do not know his frequencies or what kind of "energy" he used. The frequencies I have been using are from Dr. Nogier but the reason for trying to use the Propeller (as a step up from the Basic Stamp) is to get the frequencies more precisely tuned and to open up the possibility of experimenting with others as I become aware of them ie Schumann Resonance. I'm not aware of harmful frequencies so I found that disturbing- can you direct me to the table you mentioned or expand on harmful freqs. The unit I have now really seems to help so I am excited about making it better- I sure appreciate any help you can give me. Thanks for the links.
All the best,