If people are getting offended at seeing other teams list their accomplishments, maybe they should spend less time whining and more time doing things to make their own team win. - artdutra04 [more]
 Chief Delphi Robot Controller Digital Input
 User Name Remember Me? Password
 CD-Media CD-Spy
 portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 Thread Tools Rate Thread Display Modes
#1
01-20-2003, 12:56 PM
 crazycliffy Registered User #0846 Join Date: Jan 2003 Location: San Jose Posts: 11
Robot Controller Digital Input

The RC Digital Input is Not active (off) and set at +5V when it is not connected to ground.

The RC Digital Input is Active (On) when It is tied to ground, at 0V.

What happens when I apply an analog signal to this, from ranges from 0 to 5 volts? Does this mean that If I apply a 1.5V signal to the digital input, will the RC still think it is (Off), and thus Not Active? Obviously, If I put a 0V signal this is ground, and this is enough to trip the digital inputs?

The FullSize RC reference manual says, I can't apply a positive voltage to any of the digital inputs.. But I don't exactly know why they say we can't.

thanks for any help.
#2
01-20-2003, 09:05 PM
 Don Reid Registered User #0997 Team Role: Mentor Join Date: Jan 2003 Rookie Year: 2002 Location: Corvallis, Oregon Posts: 45
The input circuit has some threshold. If the input is below this voltage, it will be seen as low (active), above it will be seen as high (inactive). I'd have to see a schematic for the RC to know precisely what this threshold is (or run an experiment), but many common logic systems switch at about 1.4V.

It is possible that the input has "hysteresis" where the high>low threshold is lower than the low>high one.

You should also realize that the threshold is not precise, it can vary from part to part and can change with temperature, voltage, etc.

The digital inputs have some pull up circuit, probably a resistor. This could affect the output of your analog circuit depending on its design.
__________________
Don Reid
#3
01-20-2003, 11:24 PM
 Al Skierkiewicz Broadcast Eng/Chief Robot Inspector AKA: Big Al WFFA 2005 FRC #0111 (WildStang) Team Role: Engineer Join Date: Jun 2001 Rookie Year: 1996 Location: Wheeling, IL Posts: 11,071
This is very common practice for interfacing unknown inputs to a complex circuit for digital or status inputs. The input circuit is designed to look for a closing contact to ground or common. The input is designed so that no voltage need be applied from the external circuitry and therefore no crosstalk or voltage interaction that could cause the power supply of the robot controller to induce misc data in any input or affect the operation of the controller. For this reason, applying any voltage, even if it is 5 volts or less, runs the risk of causing errors or damage to the controller or it's power supply.
__________________
Good Luck All. Learn something new, everyday!
Al
WB9UVJ
www.wildstang.org
________________________
Knowledge is power. Power UP!
#4
01-21-2003, 08:57 AM
 Lloyd Burns Registered User FRC #1246 (Agincourt Robotics) Team Role: Engineer Join Date: Jun 2001 Rookie Year: 1997 Location: Toronto Posts: 292
The inputs are standard TTL or CMOS digital inputs. Their thresholds are listed in Data Sheets on manufacturers websites. No mention has been made (re IFI equipment) of Schmitt trigger inputs, which have hysteresis, and which would change things only a little.

The highest threshold they would have is CMOS's half of Vdd, with the IFI system, about 2.5 V. TTL and CMOS with TTL-compatibility will switch at around 1.25 to 1.5 V. I haven't tested which IFI has, as it seems unimportant.

Any of these inputs acts like a high impedance input, with a 1 to 100 kohm resistor (depending on logic family) pulling it up to the +5V rail. Basically, the input voltage is either 5 V (but high resistance) when open, or zero when the switch is closed to ground. If you put a resistance from input to ground that is in the range of the pull-up, the state of the output would be practically indeterminate.

When the input is grounded, the fact is reported in the rc/oi_sw bytes as a one.

Analog (slowly varying) signals cause jittery outputs when near the threshold of non-schmitt trigger inputs, and the output snaps to +5V or 0V when the input voltage is further from the threshold. For large (steep slope) analog signals, the output appears as a square wave. Depending on your analog output impedance and voltage, you could have a low, a high, some jitter, or even a serious oscillation [possibly RF] (at the threshold, where the gate is biased to linearity, the gain of ttl gates is very, very high).

Since the IFI eqipment reads the values only every 26 ms (a value posted by others elsewhere in CD), you would not read the jitter near threshold, but the value would not be reliable.

Feeding a pot or a gyro into such a digital input is a poor substitute for using the analog inputs on the other connector. They have ADCs to read the voltage. Once you have a number, your program can compare to other values.

If you apply a positive voltage, say via a switch connected to +5V, you would be taking an input already pulled up to +5V, and switching it to +5V. You'd see no change, so it won't tell you about the switch closure.

BUT, if the +5V is more than half a volt higher than the input IC's +5V, say form a separate (external to IFI) power supply that fails and goes high (eg, to 12V), or a badly adjusted op-amp, you could cause a current flow into the IC's substrate, which would damage the IC permanently, so DON'T. Yes, there are series input saftey resistors in good practice, but good practice says don't depend on them.

So... don't put your daughter on the stage, Mrs Worthington (the outcome is predictably bad), and don't apply analog signals to digital inputs (the output is unpredictably bad).

Sorry for the length.
#5
01-21-2003, 10:24 PM
 Al Skierkiewicz Broadcast Eng/Chief Robot Inspector AKA: Big Al WFFA 2005 FRC #0111 (WildStang) Team Role: Engineer Join Date: Jun 2001 Rookie Year: 1996 Location: Wheeling, IL Posts: 11,071
Quote:
 Originally posted by Lloyd Burns If you put a resistance from input to ground that is in the range of the pull-up, the state of the output would be practically indeterminate.
Thanks LLoyd,
I should add here for anyone following this thread, if the input circuitry is CMOS and if you were to encounter the above scenario, this logic family has a nasty tendency to go into a linear region (acting like an amplifier instead of a digital IC)and that causes the IC to draw high currents from the power supply.
All in all, we must use the equipment as intended, digital devices to digital inputs.
__________________
Good Luck All. Learn something new, everyday!
Al
WB9UVJ
www.wildstang.org
________________________
Knowledge is power. Power UP!
#6
01-23-2003, 06:11 PM
 rosebud Registered User #0115 (MVRT) Join Date: Sep 2002 Location: California Posts: 24
would anyone mind repeating all that above in a language a poor robotics member (that has played with circuits but hasnt taken electronics and therefore wouldnt know the names for eveything) would understand?
#7
01-24-2003, 08:45 AM
 seanwitte Registered User None #0116 Team Role: Engineer Join Date: Nov 2002 Location: Herndon, VA Posts: 378
inputs

The binary inputs are designed to be used with contact switches and no other external components. They're actually doing you a favor, but it makes it a little harder to interface TTL level inputs.

If you want to connect a switch to a pin on the stamp (not the RC) you'd need a pull-up resistor so that the pin has a stable value. When the switch is closed, the pin is shorted to ground.

The pin is internally inverted byt the RC so it sees a 0 when the switch is open and 1 when its closed. Since the input is already pulled up to +5V, applying a voltage to it won't change the value. If you apply more than +5V you'll fry it.

If you have an external circuit that you want to interface with the binary inputs, you'll need to use a component that acts like a switch. I'm sure there are other ways to do it, but I know that an NPN BJT (bipolar junction transistor) as an open-collector switch works fine. You connect the binary input to the collector pin, a ground to the emitter pin, and your logic signal to the base. You also need to connect a ground from your external circuit to the emitter pin. When your signal goes high it closes the switch and when its low it opens it. You can get a pack at Radio Shack for a few bucks.
#8
02-15-2003, 05:51 AM
 dave_l Registered User #1038 Join Date: Feb 2003 Location: Lakota East HS Posts: 10
active interface to DI?

I *REALLY* want access to the Switch 1/2/3 LEDs on the operator interface.

I have _some_ electronics knowledge, and suspected that the DIs are open collector inputs with a pull up resistor.

I am wondering how involved it would be to use say an NPN (ie current sinking) switching transistor with one of the relay outputs to switch one of the digital inputs?

If possible, I would then use some of my unused relay outputs to control DI 1/2/3 and hence the three LEDs on the OI.

Can any electronics gurus out there suggest a simple circuit?

Thanks
#9
02-15-2003, 06:05 AM
 dave_l Registered User #1038 Join Date: Feb 2003 Location: Lakota East HS Posts: 10
DUH!

What seanwhite posted just clicked with me...

Questions:

Just the bare NPN BJT transistor?
No current limiting resistor?
No biasing?

Thanks!
#10
02-15-2003, 06:56 AM
 Lloyd Burns Registered User FRC #1246 (Agincourt Robotics) Team Role: Engineer Join Date: Jun 2001 Rookie Year: 1997 Location: Toronto Posts: 292
Re: active interface to DI?

Quote:
 Originally posted by dave_l I *REALLY* want access to the Switch 1/2/3 LEDs on the operator interface. I have _some_ electronics knowledge, and suspected that the DIs are open collector inputs with a pull up resistor. I am wondering how involved it would be to use say an NPN (ie current sinking) switching transistor with one of the relay outputs to switch one of the digital inputs? If possible, I would then use some of my unused relay outputs to control DI 1/2/3 and hence the three LEDs on the OI. Can any electronics gurus out there suggest a simple circuit? Thanks
The OI Manual (.pdf from IFI) says that the switch LEDs represent the switch inputs on the RC and are not programmable in PBASIC.

On the other hand, if you used sw1 for the input from your pressure switch, for determining when the compressor should be turned on, you could see from the sw1 LED when the compressor was drawing the battery voltage down.

The "relay outputs" that show up on the OI are the signal the RC passed back to the OI. This same pair of bytes (RelayA and Relay B) are passed inside the RC to the bank of output circuits which control the relay outputs. Shorting one of these would short an output, but have no effect on the feedback bytes, nor on the LEDs. If you wish to use the relay LEDs, you'll have to use Relay1_fwd = 1, or Relay2_rev = 0, to do it

Have you thought of utilizing Out8,9,10 & 11 ? These are low-current outputs to drive your LEDs, and are available from Port1.

dave_l :

Yes just an OC NPN transistor, collector to the input, emitter to ground. Biasing in a digital connection is optional. Every RC digital input has a 10k pull-down resistor to +5V, and all the series resistance it wants, internally. for the sake of your transistor, some series resistance in the base circuit is recommended.

See the IFI site for a .pdf file of the equivalent input circuit.

This is the kind of output you have with the Banner sensors (discussed elsewhere on CD).

Last edited by Lloyd Burns : 02-15-2003 at 07:06 AM.
#11
02-15-2003, 07:38 AM
 dave_l Registered User #1038 Join Date: Feb 2003 Location: Lakota East HS Posts: 10
I'm already using all 8 of the PBASIC accessable LEDs on the OI. I want PBASIC access to the other three OI LEDS. Since they are hardwired to DI 1/2/3, I seek a way to switch those three DIs under program control. Hence my thought of wiring unused Relay Outputs to those three Digital Inputs. Thus, setting a relay out (under program control) switches the DI, resulting in control of the LED on the OI.

re: "some series resistance in the base circuit" - suggestions? couple hundred ohms?

re: "See the IFI site for a .pdf file of the equivalent input circuit" - which file? I've pulled and reviewed most of them, and can't think what you might be referring to...

re: "kind of output you have with the Banner sensors" - I'll check those docs out

Thanks again!
#12
02-16-2003, 03:28 AM
 Lloyd Burns Registered User FRC #1246 (Agincourt Robotics) Team Role: Engineer Join Date: Jun 2001 Rookie Year: 1997 Location: Toronto Posts: 292
Relay o/p are indeed 0V or 5V ! Connecting a relay o/p pin, either W/Y or R, to a digital input pin will indeed give you control of those LEDs.

I relied on the diagram IFI posted, showing the gate with 10k pullup to voltage.

BTW, a 2002 RC input switched the switch LED on the OI at 1V< Vin < 2V, so it is not a CMOS (4000 series or 74HCMOS) compatible input, unless IFI used 3V logic, and against that, the open circuit voltage of the pin is 5V. It could still be 74HCTxxx compatible.

 Thread Tools Display Modes Rate This Thread Linear Mode Rate This Thread: 5 : Excellent 4 : Good 3 : Average 2 : Bad 1 : Terrible

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts vB code is On Smilies are On [IMG] code is On HTML code is Off
 Forum Jump User Control Panel Private Messages Subscriptions Who's Online Search Forums Forums Home Announcements     User Announcements FIRST     General Forum         FIRST E-Mail Blast Archive     Rumor Mill     Career     Robot Showcase Technical     Technical Discussion     Robotics Education and Curriculum     Motors     Electrical         CAN     Programming         NI LabVIEW         C/C++         Java         Python     Control System         FRC Control System         Sensors     Pneumatics     Kit & Additional Hardware     CAD         Inventor         SolidWorks         Creo     IT / Communications         3D Animation and Competition         Website Design/Showcase         Videography and Photography         Computer Graphics     National Instruments LabVIEW and Data Acquisition         LabView and Data Acquisition Competition     Unsung FIRST Heroes     Awards         Chairman's Award     Rules/Strategy         Scouting         You Make The Call     Team Organization         Fundraising         Starting New Teams         Finding A Team         College Teams     Championship Event     Regional Competitions     District Events     Off-Season Events     Thanks and/or Congrats     FRC Game Design     OCCRA         OCCRA Q&A         OCCRA Programming Other     Chit-Chat         Games/Trivia             Fantasy FIRST     Car Nack's Corner     College & University Education     Dean Kamen's Inventions     FIRST-related Organizations         Western Region Robotics Forum         Southern California Regional Robotics Forum         The Blue Alliance             Video Archives     FIRST In the News...     FIRST Lego League         Lego Mindstorm Discussion     FIRST Tech Challenge     VEX         VEX Robotics Competition         VEX IQ     Televised Robotics     Math and Science         NASA Discussion ChiefDelphi.com Website     CD Forum Support     Extra Discussion

 Similar Threads Thread Thread Starter Forum Replies Last Post How much planning goes into your robot? Jnadke General Forum 41 01-29-2006 08:29 PM serious problem found - robot controller resets when jarred! KenWittlief Electrical 23 03-19-2003 12:30 PM Robot Digital Input Mike Norton Technical Discussion 5 01-16-2003 01:31 PM WASH Palm scouting at the Championship Mike Soukup Scouting 2 04-19-2002 02:14 PM about how Drive Train push the robot... shouldn't the force accelerate the robot? Ken Leung Technical Discussion 12 11-26-2001 08:39 AM

All times are GMT -5. The time now is 09:02 PM.

The Chief Delphi Forums are sponsored by Innovation First International, Inc.

 -- English (12 hour) -- English (24 hour) Contact Us - Chief Delphi - Rules - Archive - Top

Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright © Chief Delphi