True / False Quiz

[Richard]

Greetings group. I am a new member so please forgive me if I do or say
something that I shouldn't.
I have been asked to make a True / False quiz board. The board will
have 10 questions on it with two miniature push buttons below each
question and a Green and Red LED to display whether the correct button
was pressed. In other words if the correct response to the question is
True and the participant presses the True button the Green LED will
light up. If the participant presses the False button the Red LED will
light up.

So far this is pretty simple even for me. My problem is that I do not
know what type of "Latch" to use so that the Led corresponding to the
button that was pushed will stay illuminated after the participant
releases the button AND to dissallow the other button to have any
effect. Again in other words once the participant has pressed a button
the answer is final and they have to move on to the next question. At
the end of the quiz they can count the number of Green and Red LEDs
that are illuminated to get their score and then press a reset button
to clear all answers.

This board must be portable so I need it to run on battery power like a
9V battery.

Thanks for any and all input.

Richard

 

[default]

Greetings group. I am a new member so please forgive me if I do or say
something that I shouldn't.
I have been asked to make a True / False quiz board. The board will
have 10 questions on it with two miniature push buttons below each
question and a Green and Red LED to display whether the correct button
was pressed. In other words if the correct response to the question is
True and the participant presses the True button the Green LED will
light up. If the participant presses the False button the Red LED will
light up.

So far this is pretty simple even for me. My problem is that I do not
know what type of "Latch" to use so that the Led corresponding to the
button that was pushed will stay illuminated after the participant
releases the button AND to dissallow the other button to have any
effect. Again in other words once the participant has pressed a button
the answer is final and they have to move on to the next question. At
the end of the quiz they can count the number of Green and Red LEDs
that are illuminated to get their score and then press a reset button
to clear all answers.

This board must be portable so I need it to run on battery power like a
9V battery.

Thanks for any and all input.

Richard

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?

 

[petrus bitbyter]

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?

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

 

[Richard]

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]

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.

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 www.tech-chat.de

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

 

[Richard]

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 www.tech-chat.de

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

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

 

[petrus bitbyter]

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 www.tech-chat.de

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

| 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

 

[Richard]

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 www.tech-chat.de

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

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

 

[petrus bitbyter]

"Richard" <[email protected]> schreef in bericht

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 www.tech-chat.de

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

| 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

 

[Richard]

"Richard" <[email protected]> schreef in bericht


| 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

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