Critique my schematic

Thread Starter

redgear

Joined Oct 17, 2019
131
Beginner. Looking to get advice, suggestions and improvements for my circuit.

Initial Design.PNG

Thanks :)
Edit: Please do advice about safety and reliability of the circuit? What should be added/removed to make it more robust and reliable.
 
Last edited:

Irving

Joined Jan 30, 2016
794
Good start, nice to see a clean layout.

Put the 12v - 5v regulator in with the rest of the power supply and label the block"Power Supply", it makes no sense for it to be on its own.

Signals should flow left to right. So your switches should have +5v to left and SWx to right. I'd call that block "Inputs"

Similarly flip your UNO over so SWx comes in from left. There's no need to show the Uno and the ULN2003 disconnected like that unless Signal is going elsewhere.

Put the relay in with the lamps - thats your "Outputs" block. Some would argue that should be on RH side.

On something this simple its not really necessary to break it down, but its good practice for the future.
 

Thread Starter

redgear

Joined Oct 17, 2019
131
Good start, nice to see a clean layout.

Put the 12v - 5v regulator in with the rest of the power supply and label the block"Power Supply", it makes no sense for it to be on its own.

Signals should flow left to right. So your switches should have +5v to left and SWx to right. I'd call that block "Inputs"

Similarly flip your UNO over so SWx comes in from left. There's no need to show the Uno and the ULN2003 disconnected like that unless Signal is going elsewhere.

Put the relay in with the lamps - thats your "Outputs" block. Some would argue that should be on RH side.

On something this simple its not really necessary to break it down, but its good practice for the future.
Thank you. I will make those changes.
How reliable is the design? Do I need any more additions to make it more robust and reliable?

You need capacitors on input and output of 7805.
I am inputting the filtered output from 7812 to 7805. Do I still need them?
 

BobTPH

Joined Jun 5, 2013
2,427
Your switches leave the input pins floating. If the pins have internal pulldowns, the 10K resistors could cause an indeterminate logic level. Common practice is to connect the switch directly from the pin to ground and use an internal or external pullup.

Bob
 

Thread Starter

redgear

Joined Oct 17, 2019
131
Ditch the ULN2003 and replace it with a 2N7000 (or an NPN with suitable base resistors) unless you are planning expansion where the other drivers will be used.
Thanks. I still haven't decided if I am going to use one or four relay to drive the components.

Your switches leave the input pins floating. If the pins have internal pulldowns, the 10K resistors could cause an indeterminate logic level. Common practice is to connect the switch directly from the pin to ground and use an internal or external pullup.

Bob
Thank you. I will make the change.

True, but it will take about the same amount of power.
Why are you concerned about current?
The voltage after retification may vary from 13 to 22v due to no-load/load characteristics of transformer.
Driectly stepping down from those voltages to 5v will heatup the ic which increase and more current draw is only going to increase it.
Correct me if I am wrong. Thanks
 

crutschow

Joined Mar 14, 2008
25,117
Won't the capacitors would become expensive?
Not appreciably.
You need higher capacitance, but can use a lower voltage rating, which tends to balance out the relative cost.
And you eliminate the 12V regulator, and save some power since you no longer need to drop the 12V to 5V.
 

Thread Starter

redgear

Joined Oct 17, 2019
131
Not appreciably.
You need higher capacitance, but can use a lower voltage rating, which tends to balance out the relative cost.
And you eliminate the 12V regulator, and save some power since you no longer need to drop the 12V to 5V.
Alright, I will compare the costs and make the change.
 

Irving

Joined Jan 30, 2016
794
How do I calculate the capacitance required? Will 0.1uF work for all?
100nF ceramic is fine. As said, you need 10uF on outputs of regulators.

I'd second using MOSFET to switch relay and using 5v relay.

An alternative is use an logic input SSR rather than transistor/relay combo. Something like this or for higher power, this.


Are you planning to put this on a PCB or something else?
 

dl324

Joined Mar 30, 2015
10,944
Beginner. Looking to get advice, suggestions and improvements for my circuit.
Personally, I don't care for your style of schematic drawing. I think of it as more of a netlist because connectivity is conveyed with a bunch of net names.

At the very least, you could connect the 5V regulator to the 12V regulator and remove some of the white space.
clipimage.jpg
 

Thread Starter

redgear

Joined Oct 17, 2019
131
Personally, I don't care for your style of schematic drawing. I think of it as more of a netlist because connectivity is conveyed with a bunch of net names.

At the very least, you could connect the 5V regulator to the 12V regulator and remove some of the white space.
View attachment 212002
Thank you. Does the circuit look fine? Do I need add something to make it more safe and reliable?
 

dl324

Joined Mar 30, 2015
10,944
Do I need add something to make it more safe and reliable?
I didn't try to follow the schematic because I don't find that style conducive to understanding circuit intent.

The relay is switching neutral and the lamps are always connected to line. It would be safer to switch line with the relay. I'd also swap the positions of the switches and fuses so the switches wouldn't have line voltage if a fuse blew.
 
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