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Old 04-16-2018, 08:45 AM   #1
Dgtech
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Default My basic project - needs simplified - Digital TTL circuit maybe

OK... this simple circuit idea is kinda like the show Jeopardy.
In this case:

There will be six contestants

One button per contestant - single pole single throw

Each contestant's button will correspond to a light - one light per contestant.

The light needs to stay on and lockout other contestants from ringing in until the master reset button is depressed.

Voltage has to be low voltage, 24VDC or lower.

I tried to solve this with a basic design from my experience with relay logic. (see picture). This design would definitely work however I can't find a relay, let alone six, that has five auxilary contacts. Even if I did, it would be a wiring mess that I am looking to simplify. This design would be easy as pie if I could use a PLC (not an option).

I'm pretty sure there is an easier way to design this circuit.
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Last edited by Dgtech; 04-16-2018 at 08:47 AM..
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Old 04-16-2018, 09:27 AM   #2
Curious.George
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

Quote:
Originally Posted by Dgtech View Post
OK... this simple circuit idea is kinda like the show Jeopardy.
In this case:
There will be six contestants
One button per contestant - single pole single throw
Each contestant's button will correspond to a light - one light per contestant.

The light needs to stay on and lockout other contestants from ringing in until the master reset button is depressed.

Voltage has to be low voltage, 24VDC or lower.

I tried to solve this with a basic design from my experience with relay logic. (see picture). This design would definitely work however I can't find a relay, let alone six, that has five auxilary contacts. Even if I did, it would be a wiring mess that I am looking to simplify. This design would be easy as pie if I could use a PLC (not an option).

I'm pretty sure there is an easier way to design this circuit.
Do you allow for ties? I.e., what granularity of time do you want to support (ties happen when two events occur in the same time quantum -- nearly improbable in "real time" as there are usually skews between events if you can see fine enough detail)

Once you've decided this, you can then implement a sequential machine that scans the inputs (in some "fair" order) and stops on the first "hit".

An MCU would be the most straightforward (if you have tools/experience). But, you can "hard code" it in logic for not much more effort (though more "signals").

You'll also have to give consideration to potential damage from induced voltages on your (undoubtedly long) wires to the pushbuttons and indicators.
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Old 04-16-2018, 11:44 AM   #3
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

a 74ls174 and a bunch of diodes.
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Old 04-16-2018, 11:53 AM   #4
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

Just use some optocouplers at the end .... user pushes button, voltage goes in optocoupler, led turns on and the sensor on the other send picks up and sends the state to the micro

make it for 8 inputs and 8 outputs , one full port ... first 6 are user, the 8th is always rearm/reset ...

literally a few lines of code in an arduino.
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Old 04-16-2018, 04:23 PM   #5
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

You can always bank a whole bunch of relays together(hook three DPDT relays' coils in parallel) but that would make the wiring mess even tougher. Best to use a microcontroller or other programmable logic to reduce wire complexity.

However the circuit presented does not appear to be latching. I think you'll need yet another contact (perfect for three DPDT's) to latch the output on... But this means 18 DPDT relays, plus individual timing between relays could cause a bit of skew...

PLC/microcontroller will hide away a lot of this ugly complexity, at least speed it up well past human response time!
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Old 04-16-2018, 07:49 PM   #6
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

Quote:
Originally Posted by stj View Post
a 74ls174 and a bunch of diodes.
That 74ls174 looks promising. The 74ls175 may work too as seen on the same datasheet.

This year marks 20 years since I've done my digital project in tech school so... my logic is rusty.
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Old 04-16-2018, 11:01 PM   #7
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

I think just using a 'LS174 would require quite a bit of logic to work out...

How about this? No guarantees, implied or otherwise.

Oops used the wrong unit numbers. Anyway,

BOM:
3x 74LS73
6x LED
7x momentary pushbuttons
1x 74LS21
13x 470R

The problem I have with this design is that two people have a slight ~15ns advantage during tie conditions... this can be fixed with more parts to hook up. I forgot the other problem I had wasn't a real problem due to the flop nature.
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Old 04-16-2018, 11:48 PM   #8
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

New version (well, both versions).

This second one using the LS174. I do NOT like this one and not sure if it actually works due to the race condition presented. The input RC delay tries to fix the race but could allow ties if the RC is too long. The tie window currently in the microseconds, unlike the other one which has nanosecond tie resolution.

BOM:
7x momentary switch
1x74LS174
14xDiode
6x LED
1x100R
7x470R
1x1nF
1x2sc1815

Problem with this design: Holding buttons down during reset release will trigger and tie...
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Last edited by eccerr0r; 04-17-2018 at 12:01 AM..
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Old 04-16-2018, 11:48 PM   #9
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

Quote:
Originally Posted by Dgtech View Post
That 74ls174 looks promising. The 74ls175 may work too as seen on the same datasheet.

This year marks 20 years since I've done my digital project in tech school so... my logic is rusty.
[Note that polarities of signals can -- should -- be changed. But, I present them here in "positive logic" for ease of explanation]

Each button is conditioned appropriately for the environment and its edges debounced and "squared up" yielding a positive going edge when the button is pressed. This might be something as simple as a small RCD network on the input to a schmitt trigger.

All "conditioned" inputs feed a wide OR gate. The output of the OR gate clocks a D FF with the D input held HIGH. So, the leading (positive going) edge of any button press causes the FF to be "clocked to one".

Simultaneously, all inputs broadside load an edge-triggered latch. The outputs of the latch drive the individual bulbs through appropriately sized hammer drivers (HIGH == ON). The latch is clocked by the Q output of the D FF.

The latch and D FF are (asynchonously) forced "clear" with the Master Reset button.

Press and release Master Reset button. All latches go to '0'. All lights go out.

All "contestant buttons" must be released before you start the cycle!!

The first button press hereafter drives the output of the OR gate HIGH. This clocks the D FF setting the output HIGH. The rising edge of this output clocks the latch, capturing the state of the inputs (buttons).

The D FF's sole purpose is to guard against the case where folks are pressing their buttons furiously (as can be seen on Jeopardy!) resulting in more than one "clock" passing through the OR gate; the D FF can only be "set", once (until a Master Reset) and thus only delivers one rising clock edge to the latch.

Note that if two folks happen to press their buttons within some small combinatorial delay of each other, it is possible that two lamps will light. This circuit captures that event and lets the "judge" rule on the "tie".
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Old 04-17-2018, 09:14 AM   #10
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

oh fsck. I just realized my LS174 circuit has a big flaw and will not work. "Bogus points" for people to tell what the problem with the rev2 circuit is before I feel like fixing it
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Old 04-17-2018, 11:18 PM   #11
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

This should work better and should actually work, I hope...

BOM changed.

1x74LS174
8x470R
14x1n4148
1x2sa733
7xmomentary pushbuttons
1x1nF
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Old 04-18-2018, 10:14 AM   #12
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

OMG found another potential problem with the "new" LS174 "solution" ... Ugh. Forget it, use the one without a zillion diodes ...

Once again someone point out the problem I see for "bogus points"

It might actually still work however, if one resistor has enough resistance and the transistor's gain is high. This shall be the hint.

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Old 04-19-2018, 08:02 AM   #13
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

Sounds like an ideal use of an octal latch like the 74LS373.

Input pins D0-D5 are held high by R1-R6 which is reflected on output pins 0-5 keeping LEDs D7-D12 off.

Suppose, for example, S4 is momentarily pressed. This will pull pin 8 (D3) low. The corresponding output pin 9 (O3) will also go low, lighting LED D10. At the same time Latch Enable (LE) pin 11 is pulled low through diode D4, latching the output pins to their current state. Any further button presses of S1-S6 will have no effect on the output pins of the 74LS373 as they are now latched. LED D10 will remain lit until the circuit is reset. A normally closed momentary push switch (push to open) could be placed in line with the +5v line as a reset.

The 74LS373 can sink around 26mA per output, so is just about enough to drive standard LEDs directly. Any LEDs that require more current (high brightness etc.) might need an extra driver stage.

S1-S6 are momentary, normally open, push to make switches.

p.s. why are all the switch symbols in DipTrace so big! They look so out of proportion with the rest of the circuit.
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Old 04-19-2018, 10:28 AM   #14
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

Ah... just omitted from the circuit n/m.

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Old 04-19-2018, 04:36 PM   #15
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

My original idea to reset the circuit was to simply have a momentary push to break switch in the 5v supply (Quiz_buttons2.pdf), but that always seems like a bit of a bodge for some reason.

Putting the momentary switch between pin 11 (LE) & the anodes of D1-D6 (Quiz_buttons3.pdf) should release the latch, & take all the output pins high again, ready for the next "fastest finger".
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Last edited by Radio Fox; 04-19-2018 at 04:50 PM..
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Old 04-19-2018, 05:29 PM   #16
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

Yeah I was thinking about the #3 version for the reset after rereading your text, though #2 would work too and agreed that seems a bit of a bodge. Anyway yeah LS373 should work better than the LS174 which needed a messy hack to utilize...
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Old Yesterday, 11:19 AM   #17
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

Couldn't stand those silly button symbols any longer.

Used DipTrace's component editor to design some better looking ones.
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Old Yesterday, 09:35 PM   #18
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

Old fashion latching:
http://www.techlib.com/electronics/games.html

https://electronicsclub.info/p_quiz.htm

Or QUIZ-O-TRON 3000: ARDUINO QUIZ CONTESTANT LOCKOUT SYSTEM
http://www.instructables.com/id/Quiz...tant-lockout-/

Search:
'arduino jeopardy game'
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Old Today, 07:38 AM   #19
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

Quote:
Originally Posted by budm View Post
We tend to forget about old fashioned disrete components these days. If we want to latch a bulb, then why not use a latching component (SCR) to do so!

It will only work for incandescent bulbs though, as it relies on the short circuit of the incandescent bulb to supply the contestants circuits, and thereafter (once a button has been pressed), to remove the gate supply to the other SCRs by halving the main voltage.

Nice, simple, modular design though.
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Old Today, 09:22 AM   #20
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Default Re: My basic project - needs simplified - Digital TTL circuit maybe

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We tend to forget about old fashioned disrete components these days. If we want to latch a bulb, then why not use a latching component (SCR) to do so!
The problem with discrete components is that they tend to have very little "value added" potential. You can turn on a lamp with an SCR/thyristor but can't do much beyond that (for that "lamp application").

Yeah, you can add an RC and get some control over conduction angle -- and, thus, a "dimmer". But, only to the tolerances of the components used (try restoring a lamp to a previous intensity; try dimming two lamps to the same intensity; try dimming two different lamps to the same intensity; etc.). Adding any additional functionality/features directly increases the cost of the product (DM+DL).

Hence the move to use discretes only for those things that have specific high power/current/voltage requirements and all of the "functionality" in ASICs or MCUs.

I suspect we are already close to the point where folks who can't code (or, at least think in terms of algorithms) have greatly reduced market opportunities. (I watch my "analog" friends throw fits any time they're tasked with something as simple as "precise" timing in a design -- a bit of logic creeps in, eventually replaced with a microcontroller or ASIC, and then the assault on removing suddenly unnecessary "discretes" begins!)

Note the "jeopardy" problem is a smaller aspect of a "pinewood derby" race timer; "who finished in first place?" Imagine modifying one of these solutions to add the ability to rank the first three finishers! Then, augment that functionality by noting their actual race times... (with an MCU, the design doesn't significantly change -- esp in recurring costs!)
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