Trying to track down schematics for an old Maplin kit. GH49D quiz buzzer.

Thread Starter

matt_hooks

Joined Apr 26, 2020
2
Hi. Total beginner to the forum. I'm getting back in to electronics as a hobby after many years away.

I was given an "old" (I have no idea of the actual year of manufacture but it looks like the board design might be from 1994?) kit for a quiz buzzer.
Unfortunately, although it appears to have all the components, the circuit diagram/assembly instructions have been lost over the years.

The kit uses a ULN2803A transistor array, one HCF4098BE (Google says this is a monostable multi-vibrator) and two HCF4043BE (QUAD NOR 3-STATE R-S LATCHES).

Does anyone have any idea where I might track down the circuit diagram for this, before I have to start trying to reverse engineer it? I've contacted Maplin but, unsurprisingly they don't have access to this kind of info from the old company.

Any help most gratefully received.
Matt
 

AnalogKid

Joined Aug 1, 2013
9,498
Photos of both sides of the pc board?

Reverse engineering this circuit should be relatively easy. How many switch inputs? Besides the buzzer, any other outputs (LEDs. etc.)? Is there a reset/restart switch input?

Generically, this is called a game show circuit. There are many example schematics on the web and in threads on this forum.

ak
 

Thread Starter

matt_hooks

Joined Apr 26, 2020
2
Photos of both sides of the pc board?

Reverse engineering this circuit should be relatively easy. How many switch inputs? Besides the buzzer, any other outputs (LEDs. etc.)? Is there a reset/restart switch input?

Generically, this is called a game show circuit. There are many example schematics on the web and in threads on this forum.

ak
I'll get some pics up tomorrow evening, as well as a list of all the components. :)

It looks like it's a simple enough setup. It doesn't have any peripherals, and no switches or lights on the board. The only on board output is a buzzer. I'm assuming it will need answer and reset buttons, with whatever lights are required, making and adding. I don't really have any use for it, but kind of feel honour bound to get it working as it was a gift from a friend.
 

djsfantasi

Joined Apr 11, 2010
7,930
Thanks for posting the article. Unfortunately, the ‘schematic’ isn’t detailed enough to grok the circuit without a lot of work, redrawing it as a electronic schematic rather than a hobby diagram. Someone might do that but I’m too busy right now.
 

djsfantasi

Joined Apr 11, 2010
7,930
An electronic schematic doesn’t use a pin diagram of logic ICs. Without the gate wiring, it is difficult to tell what the circuit is doing. 555s are common enough that this isn’t a problem. Usually, when showing logic (AND, OR, NOT, NAND, NOR, etc...) the actual gate wiring is expected. I could redraw it to show that wiring, but I’m in a lazy mood today.
 

KMoffett

Joined Dec 19, 2007
2,918
That's your definition. For the hobbyist interested in duplicating that circuit, it would be easier to wire according to the IC's pin out. If you want to understand the function and relationships of all the internal logic elements then you would need the learn the elements of each chip. For example if you google the CD4098 datasheet you will get two "blocks" for the two monostables, not the internal logic gates of each of the two monostables. There are as many levels of detailed "electronic schematics" as needed for each specific audience. The first block diagram on that page would be sufficient for a person wanting duplicate it in a microcontroller design. If you can't find what you want, then you will need to put in the effort...as we have already have. Sorry, but that's life.
 

AnalogKid

Joined Aug 1, 2013
9,498
I side with dj on this one, although it gets a little fuzzy with complex single-function parts like the 4098. for that there should at least be function names at each pin location.

A schematic diagram and a wiring diagram are two different things, intended to convey different information for performing different functions. Yes, there can be a lot of overlap, but in round numbers a schematic controls the design, while a wiring diagram controls the assembly, A schematic conveys the intent of the designer and describes the performance of the circuit. Once you gain some experience in reading schematics, you will find that a good schematic is way better than text in telling you whatever it is you need to know about the circuit, in much less time that reading a bunch of text. There are threads in this and other fora that go on for 20 or 30 posts trying to get a handle on the question; then the TS posts his schematic and everything is cleared up almost immediately.

Of course this can't be a 100% all the time rule, but if you get the distinction built into your project thinking at an early stage (or early age), it will serve you well as your knowledge and circuit sophistication grow. In particular, when using multi-section parts such as a dual opamp or a quad NAND gate, always use multiple occurrences of the internal function symbol rather than a box with sequential pin numbers around the sides. A logic diagram drawn that way is useless.

ak
 
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