Pin conservation, sneaky modulating tricks?

Jason Smith

I'm creating a game show buzzer, and have hit a hurdle in that I need more pins than I have available. I use 3 pins for the buzzers (1 each), 4 pins for LEDS to indicate status (player 1,2,3 buzzed, and buzzer ready). Status updates are sent to the computer via serout, so I need those pins too. Now I have 3 judge panels, with three buttons each (thus requiring 9 pins) that I need to read. Is there some quick and clever way to use one pin for the three buttons? Maybe some easy way to create an oscillating signal I can interpret?

Mike Green

Basically, you can use the RCTIME statement to measure a resistor. Each judge panel has 3 switches with a different resistor in series with the switch, the 3 resistor/switch combinations are connected in parallel to form the resistance R as shown in the Stamp manual in the section on the RCTIME statement and the Stamp can tell which one (or none) were chosen. It can't determine if more than one is pressed ... That's why you'll need one pin for each panel. Typically, you'll use 3 resistors with each one 2-4 times the value of the previous, like 4.7K, 10K, 22K (with a 0.1uF capacitor). These will give you 3 different values (plus "infinite" ... for no button) from the RCTIME statement.

If that won't work for you, use a 74HC165 serial shift register to expand the Stamp's input pin capability. There's a discuss of this and some programming examples in the StampWorks manual that you can download.

Post Edited (Mike Green) : 8/16/2007 5:11:43 PM GMT

D Faust

I would use the RCTIME idea.· Use larger resistors as Mike said, otherwise the RCTIME command will take longer.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

LOOKDOWN ThisThread, [noparse][[/noparse]Your_?, My_?, Cool_Thing], looknum
LOOKUP looknum, [noparse][[/noparse]1, 2, 3], subnum
ON subnum GOTO Hope_this_helps, Thanks!, WOW!!
END 

Jason Smith

wow! quick reply and great suggestion, this will work perfectly (assuming I don't mess it up) as I only need to know which button was pressed, multiple buttons will not be pressed at once. Thanks!

Mike Green

To simplify things, I'd put a 100K resistor across the capacitor in the diagram. This provides for 4 discrete resistor values rather than 3 and "infinite". The parallel 100K won't affect the other resistances much.

Vern Graner

Jason Smith said...
Is there some quick and clever way to use one pin for the three buttons?

You could use the 74LS165 multiplexer chip to read up to 8 inputs with only 3 pins.

There are schematics and source code examples detailed in the Stamp Works article available on Parallax's web site here.

I used this with great success in my RoboSpinArt project. The 74ls165 reads four direction joystick switches and four pump activation switches.



Vern

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
Senior Systems Engineer    | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com        | is up, then we obviously don't need
Austin Office 512 328-8947 | you, so why are we paying you?" ©VLG

David H.

If you just need more IO pins, you could use the BASIC Stamp 2p40 module.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
David


There are 10 types of people in this world,...
Those that understand binary numbers, and those that don't!!!

TechnoRobbo

You could daisy chain several 74HC165 to get many inputs out of 3 pins.

3 chips will give you 24 inputs from 3 pins!

And while your at it get some 74HC595 and do the same with the outputs.

·Parallax sells them:

http://www.parallax.com/detail.asp?product_id=602-00010

http://www.parallax.com/detail.asp?product_id=602-00009


▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Have Fun


TR

Post Edited (TechnoRobbo) : 8/19/2007 4:14:53 AM GMT

D Faust

Is a shift register the same thing, as a serial to parallel chip?· Thanks.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

LOOKDOWN ThisThread, [noparse][[/noparse]Your_?, My_?, Cool_Thing], looknum
LOOKUP looknum, [noparse][[/noparse]1, 2, 3], subnum
ON subnum GOTO Hope_this_helps, Thanks!, WOW!!
END 

TechnoRobbo

yes - Shift register is what they call it on the datasheets
[url=:openreq('http://www.ortodoxism.ro/datasheets/philips/74HC_HCT165_CNV_2.pdf')][/url]

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Have Fun


TR

D Faust

thanks!

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

LOOKDOWN ThisThread, [noparse][[/noparse]Your_?, My_?, Cool_Thing], looknum
LOOKUP looknum, [noparse][[/noparse]1, 2, 3], subnum
ON subnum GOTO Hope_this_helps, Thanks!, WOW!!
END 

pwillard

Some of Jon's N&V articles also point out the use of I2C Chips like the PCF8574... you only lose 2 pins and you can attach quite a few other different I2C devices to the same bus.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔

---

There's nothing like a new idea and a warm soldering iron.