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basically i have this circuit diagramcircuit.png for a digital alarm clock but i dont really understand the circuit like things like why each component is there and whats its purpose. i only understand the obvious component like the thermistor is there to sense temperature i just need someone tell me the answer to what the purpose is for the main component like why is there resistors connected the way it is and stuff like that

thanks in advance!
 
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SparkyChick

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Is this a school/college/homework project? If so, you should have an attempt. I'm reasonably confident I could explain most of it to you but I'm not just going to and potentially do your homework for you.

Have an attempt and post it and then we'll give you feedback and point you in the right direction.

You can do a bit of searching on google... using the part numbers provided.

As for the exact purpose of some parts, that could be a bit difficult as some of it will depend on the firmware.
 

davesparks

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Which specific parts do you need help with?

Resistors have a few different uses, the row of resistors connected to the displays are there to limit the current through the LEDs in the display.
The resistors in series with the LDR and thermistor are creating potential dividers.
There's anothe resistir acting as a pull up to keep and input at a solid +5V when the input is not being made low, this prevents the input from floating.
 

static zap

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Start with getting a grip with current , voltage , resistance and sharing voltages proportionally between 2 parts =
a potential divider.
I overheated my Maplins version making R16 more sensitive ! (>25 yrs ago)
 
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Is this a school/college/homework project? If so, you should have an attempt. I'm reasonably confident I could explain most of it to you but I'm not just going to and potentially do your homework for you.

Have an attempt and post it and then we'll give you feedback and point you in the right direction.

You can do a bit of searching on google... using the part numbers provided.

As for the exact purpose of some parts, that could be a bit difficult as some of it will depend on the firmware.
Yes iv tried iv googles datasheets to give me an ideas of what pins do what but some are very technical i only understood things like gnd,vcc etc. I would never post on a thread asking for help if i didnt have a go myself
Post automatically merged:

Which specific parts do you need help with?

Resistors have a few different uses, the row of resistors connected to the displays are there to limit the current through the LEDs in the display.
The resistors in series with the LDR and thermistor are creating potential dividers.
There's anothe resistir acting as a pull up to keep and input at a solid +5V when the input is not being made low, this prevents the input from floating.
I need help with stuff like what is the function of that 8 pin ic?
why is there transistor at the top?
Basically if someone asks me how this circuit works i can tell them like current travels from ... into here and this turns on .....
etc.
 
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It sounds like you basically want to learn electronics. While that is a very noble aim, it is going to take a whole lot more than a few answers on a forum to achieve that!

I am out of touch on books, etc, to suggest as a beginner's guide for electronics, but possibly the single most useful book I have found to recommend is "The Art of Electronics" by Paul Horowitz & Winfield Hill.


If you find a copy of the 2nd edition it is still very good.
 

davesparks

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Yes iv tried iv googles datasheets to give me an ideas of what pins do what but some are very technical i only understood things like gnd,vcc etc. I would never post on a thread asking for help if i didnt have a go myself
Post automatically merged:


I need help with stuff like what is the function of that 8 pin ic?
why is there transistor at the top?
Basically if someone asks me how this circuit works i can tell them like current travels from ... into here and this turns on .....
etc.
The transistors are used to switch each display on and off in sequence, many times per second.
This is called multiplexing.
The microcontroller switches on display one and outputs the required sequence on a-g then switches it off and does the same for display 2 etc etc.
As this is done many times per second the human eye does not see them flashing, it just see's the display as being permanently on.
 

SparkyChick

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The 8 pin IC is a real time clock, from the part number it's probably a Dallas part (now Maxim I believe). This maintains the time (notice there is a battery to power it) using a crystal to provide a known frequency which is divided internally to drive the internal clock.

The microcontroller communicates with this using a 3 wire serial interface, so periodically, the microcontroller will ask for the time and then drive the display through multiplexing as @davesparks has explained.

Without knowing exactly what the firmware is in the microcontroller we can only guess at the exact function. But looking at it, R16 is a light dependent resistor, possibly to dim the display when the room is dark (this would be done by changing the duty cycle on the multiplexing for the display, so instead of each display being on for say 0.01s, they are only on for 0.005s and thus appear darker), R17 is a thermistor, so maybe the clock has a temperature function. These are connected as voltage dividers between 5v and gnd and would be sampled using the analogue to digital converter in the microcontroller.

P1 looks like it might be the programming connector to flash the microcontroller with the firmware.

S1 and S2 are the function switches. When they are pressed, the pull the input pin to ground (0), so they have internal pull up resistors in the microcontroller. These would be read by the firmware which would take the relevant action.

Beyond that, it's really a deep dive into the datasheets of the devices to understand what each pin is capable of and how that ties up with what it's connected to.

So for example....

1585229616753.png

U2 pin 4 is labelled as P1.1/ADC1, which suggests to me that it can be bit 1 of digital IO port 1 and the input for analogue to digital converter 1. How it's connected suggests it can also be the data line for a 2/3 wire serial interface as it's connected to the I/O pin of the clock. So this will be toggled high (5v) and low (0v) in sync with the clock pin (SCLK) during data exchange between the two chips.

To be able to fully understand this, you're going to need to read and understand the datasheets for the devices.
 

telectrix

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The 8 pin IC is a real time clock, from the part number it's probably a Dallas part (now Maxim I believe). This maintains the time (notice there is a battery to power it) using a crystal to provide a known frequency which is divided internally to drive the internal clock.

The microcontroller communicates with this using a 3 wire serial interface, so periodically, the microcontroller will ask for the time and then drive the display through multiplexing as @davesparks has explained.

Without knowing exactly what the firmware is in the microcontroller we can only guess at the exact function. But looking at it, R16 is a light dependent resistor, possibly to dim the display when the room is dark (this would be done by changing the duty cycle on the multiplexing for the display, so instead of each display being on for say 0.01s, they are only on for 0.005s and thus appear darker), R17 is a thermistor, so maybe the clock has a temperature function. These are connected as voltage dividers between 5v and gnd and would be sampled using the analogue to digital converter in the microcontroller.

P1 looks like it might be the programming connector to flash the microcontroller with the firmware.

S1 and S2 are the function switches. When they are pressed, the pull the input pin to ground (0), so they have internal pull up resistors in the microcontroller. These would be read by the firmware which would take the relevant action.

Beyond that, it's really a deep dive into the datasheets of the devices to understand what each pin is capable of and how that ties up with what it's connected to.

So for example....

View attachment 56632

U2 pin 4 is labelled as P1.1/ADC1, which suggests to me that it can be bit 1 of digital IO port 1 and the input for analogue to digital converter 1. How it's connected suggests it can also be the data line for a 2/3 wire serial interface as it's connected to the I/O pin of the clock. So this will be toggled high (5v) and low (0v) in sync with the clock pin (SCLK) during data exchange between the two chips.

To be able to fully understand this, you're going to need to read and understand the datasheets for the devices.
i understood half of that :p :p :p . my electronics education ended in 1970. just when we'd got the hang of transistor circuits as opposed to valves, some clown went and invented the integrated circuit.
 
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  • #10
The 8 pin IC is a real time clock, from the part number it's probably a Dallas part (now Maxim I believe). This maintains the time (notice there is a battery to power it) using a crystal to provide a known frequency which is divided internally to drive the internal clock.

The microcontroller communicates with this using a 3 wire serial interface, so periodically, the microcontroller will ask for the time and then drive the display through multiplexing as @davesparks has explained.

Without knowing exactly what the firmware is in the microcontroller we can only guess at the exact function. But looking at it, R16 is a light dependent resistor, possibly to dim the display when the room is dark (this would be done by changing the duty cycle on the multiplexing for the display, so instead of each display being on for say 0.01s, they are only on for 0.005s and thus appear darker), R17 is a thermistor, so maybe the clock has a temperature function. These are connected as voltage dividers between 5v and gnd and would be sampled using the analogue to digital converter in the microcontroller.

P1 looks like it might be the programming connector to flash the microcontroller with the firmware.

S1 and S2 are the function switches. When they are pressed, the pull the input pin to ground (0), so they have internal pull up resistors in the microcontroller. These would be read by the firmware which would take the relevant action.

Beyond that, it's really a deep dive into the datasheets of the devices to understand what each pin is capable of and how that ties up with what it's connected to.

So for example....

View attachment 56632

U2 pin 4 is labelled as P1.1/ADC1, which suggests to me that it can be bit 1 of digital IO port 1 and the input for analogue to digital converter 1. How it's connected suggests it can also be the data line for a 2/3 wire serial interface as it's connected to the I/O pin of the clock. So this will be toggled high (5v) and low (0v) in sync with the clock pin (SCLK) during data exchange between the two chips.

To be able to fully understand this, you're going to need to read and understand the datasheets for the devices.
thanks you so much! you dont know how much that has helped really appreciate it!
 

freddo

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I am out of touch on books, etc, to suggest as a beginner's guide for electronics, but possibly the single most useful book I have found to recommend is "The Art of Electronics" by Paul Horowitz & Winfield Hill.
If you buy one make sure it is a genuine copy, there are loads of very poor quality fakes of this book being sold.
 
Get it from Foyles :)
I used to love the original Foyles bookshop on Charing Cross Road... before they organised all the stock onto shelves... in order. It's an enormous shop and used to have just about every book EVER printed... or at least, that's how it appeared. Rammed full !!
 
And there was that emporium on the opposite side of the road on the corner that sold second hand books "Fly Fishing by JR Hartley" anyone?
 
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