True / False Quiz

Goggle Groups poster

Use a TO92 case SCR in the ground leg of the LED circuit. Push button sends + voltage to gate via a 1 K resistor. The anode of (each) the SCR also has a steering diode to every other SCR gate - which takes them low to prevent subsequent LEDs from coming on.

Each True and each False scr anode has a set of diodes that goes to every other scr gate

Obviously, each LED will have its own current limiting resistor too.

Single PB breaks circuit to reset it.

This scheme will work as long as there aren't too many "contestants" - beyond that the wiring interconnects and number of diodes get unwieldy quickly - but you're talking portable and battery power so how complex could it be?

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----

The #1 Newsgroup Service in the World! 120,000+ Newsgroups

----= East and West-Coast Server Farms - Total Privacy via Encryption =----

"default" schreef in bericht news: snipped-for-privacy@4ax.com...

Mmm... That's 380 diodes for ten pairs of switches and LEDs. A *lot* of diodes plus 1 kg or so of copper wire. I doubt it will work the way the OP asks for.

Some years ago I'd use some 74xx74 D-type flipflops. Two flipflops in one chip can make a good mutual excluding memory cell. That's ten ICs for the memory plus twenty resistors. (Plus twenty resistors for LED current limiting.) In this simple plan, the questions can be answered at random, but once answered it cannot be changed. Not until the mastereset had been pressed that is. Buttons and LEDs are hardwired so a "true" button always activates the corresponding LED. If you want to be able to change that, you need to add (hidden) switches or straps. To minimize power requirements, I'd use CMOS logic and low power LEDs. A 9V battery may be enough for some hours.

These days, I'd go for some micro. Let's say a 28 pins one. Some ten or twelve resistors and 5 diodes (plus the LEDs ans switches off course) is all the hardware you need for the basic function. But... You have to know how to program it.

petrus bitbyter

Some years ago when I used to play around with TTL logic circuits I too would have used 74xx74 chips but it has been many years since I have played with electronics that I feel like a newbie in the industry

I was looking at the SN74LS373/374 but am sorry to say that due to my lack of keeping in touch with digital devices I do not know which one to use and/or how to use it.

petrus bitbyter wrote:

All eight latches/flipflops 74LS373/374 will be latched/clocked at the same time. No use for them in this function. As you know the 74LS74, you will understand the schematic below. (Use fixed font like Courier.) For low power consumption use 74HCT74 for instance.

+-------+----------+----+-------------+----+5V | | | | | | | | | | .-. .-. .-. .-. .-. | | | | | | | | | | | | | | | | | | | | '-' '-' '-' '-' '-' | | | | | | | | | | | | V | V | | -LED | -LED | | | | | | | +--------)----)-------------+ | | | .---. | | .---. | | | +-|D Q| +----)-----|D Q| | | +---|> | | +-----|> | | | | | R |o-+ | | R |o--+ | | '-o-' | '-o-' | | | | | +-------)-----+---------)-------+ | | | | | | o | o | o | |=| |=| |=| o | o | o | reset| |true |false | | | +-------+---------------+-------------+- | === GND created by Andy´s ASCII-Circuit v1.24.140803 Beta

You may look for the old CD4013B as well. These can handle 5-15V supply voltage so you don't need a 5V regulator. But beware. They have active high reset inputs.

BTW don't top post. It's _not_done_ in this group.

petrus bitbyter

me

wer

gh

Thank you for the diagram. That is more along the lines of what I had in mind. Can you please suggest a resistor value for the push button current limiters? I can figure out the LED current limiters after I decide on which LED's to use.

Richard

"Richard" schreef in bericht news: snipped-for-privacy@j72g2000cwa.googlegroups.com...

| Thank you for the diagram. That is more along the lines of what I had | in mind. Can you please suggest a resistor value for the push button | current limiters? I can figure out the LED current limiters after I | decide on which LED's to use. | | Richard |

CMOS logic has very high input resistances. So you can keep those resistors pretty high which will save some power. Values between 10k and 22k will do perfectly. Higher values may do but your inputs will become more sensitive for external disturbances. Of course, depending on environmental circumstances and the length of the wires/traces.

petrus bitbyter

one

the

m,

ays

s,

is

how

me

wer

gh

Sorry to add yet another request but when I look at the data sheet for the Texas Instruments SN74LS74A the pinout names appear to be different than the ones you used in your drawing. I would appreciate it if you would clarify which pins are which in your drawing. TI shows these Pin Names per circuit CLR(low) D CLK PRE(low) Q Q(low)

Your drawing Texas Instruments Description Pin Name R =3D To LED D =3D To opposite LED > =3D To T/F buttons o =3D To Reset button

| Sorry to add yet another request but when I look at the data sheet for | the Texas Instruments SN74LS74A the pinout names appear to be different | than the ones you used in your drawing. I would appreciate it if you | would clarify which pins are which in your drawing. | TI shows these Pin Names per circuit | CLR(low) | D | CLK | PRE(low) | Q | Q(low) | | Your drawing Texas Instruments Description Pin | Name | R = To LED | D = To opposite | LED | > = To T/F | buttons | o = To Reset | button | |

Well,

DATA = D CLR(low) = R (for Reset) PRE(low) = active low PREset (not drawn, connect to +5V) CLK = > (Clock input) o (to reset) = means active low, like for /Q Q = flip flop output (no connection drawn) Q(low) = /Q or Q-inverted output (not shown but connected)

-->|--- = diode symbol, "LED" added due to lack of arrows (when drawn verticaly either V and - or ^ and - are used so: | | | | V - - ^ | | | | ) reset, true and false are NO (Normaly Open) pushbuttons.

pinout: name ff1 ff2 CLK 3 11 D 2 12 Q 5 9 /Q 6 8 CLR 1 13 PRE 4 10

FAIK the pinouts for LS74 and HCT74 are the same.

Use fixed font to look at the tables.

petrus bitbyter

of

the

at,

me

or

oo

Thanks again Petrus. I think I can handle it from here. Did I forget to mention that I am "Electronically Challenged"? I used to play around a lot with digital logic electronics many many years ago and I guess old age and lack of involvement have drained me of the little that I did know!

Richard

Richard