PCB etching and basic schematic

Thread Starter

ELECTROFLUX

Joined Aug 7, 2015
38
Start with something simpler for a first circuit, get used to drawing readable schematics and routing PCBs ( if your intention is to fab a PCB at home), don't rely on the auto-router.

Small steps grasshopper.

The chances of failure, frustration and quitting are greater the larger the first project is.
Yes i understand what you mean, thanks for the suggestion, but i picked this particular project because it's something i will need in the future to come, as part of a vending machine, i didn't pick it just to see if i can do etching or build up a random circuit correctly.
 

Thread Starter

ELECTROFLUX

Joined Aug 7, 2015
38
The R (rotate) key did not work, or X or Y for mirror?
Max.
Somehow i couldn't locate the right transistor, but i found a way to rotate the one i managed to get, i have never used this program before either, but today i just learned a couple of new things and managed to find the ones i was originally looking for :)
 

Thread Starter

ELECTROFLUX

Joined Aug 7, 2015
38
As much as I'd like to machine some triple clamps on my cnc machine, I've got a long way to go before I can do that. Little steps, but if you want to jump in feet first without some skills doing the basics....well be my guest, I can only offer advice.
Agree, doing stuff with a sketchy knowledge might not suit everyone, and often rely on a bit of luck too, however, i made my choice out of life's experience, because if i had to be an expert for all the things i had been doing so far, several life wouldn't be enough, so, considering that for the time being i have just got only one life to live, i have to be practical and reduce to the bare minimum some of the many aspects involved into this, and as the success rate it's usually much higher than failures, i will keep going this way, giving more time to the things i am really interested to.
My method and preferences might not suit everyone, so, each person has got to take its own conclusions from personal's experience/taste.
Suggestions and corrections are always welcome though, especially when needed, i just learned a couple of new things from this thread and done some corrections, so thanks for it, if all goes as planned i will be able to add this project on the list of the successful ones thanks to your help, really appreciated it ;)
Ohh also, let's not forget that this it's all of public domain, so everyone interested will be able to recreate it at will and with the minimum effort once all the info have been gathered and put together.
 

Phil-S

Joined Dec 4, 2015
238
Zero ohms links are fine and widely used in commercial products.
A 2-layer board doesn't actually take much more effort, but could be ambitious if this is a first attempt.
To go from one layer to another on a 2-layer board, use via's. Commercial PCBs will have "plated through" holes in the board, but via pins are also used. I get them from Vero Technologies and they just snap off in the hole and get soldered - they look like very small nails.
I hope you've done a rough prototype as well, as you don't want to go to a lot of trouble then find problems.
Good luck anyhow
 

PhilTilson

Joined Nov 29, 2009
131
Start with something simpler for a first circuit, get used to drawing readable schematics and routing PCBs ( if your intention is to fab a PCB at home), don't rely on the auto-router.

Small steps grasshopper.

The chances of failure, frustration and quitting are greater the larger the first project is.
This is VERY good advice!

Without wishing to dampen your enthusiasm, it's clear that you are very new to circuit design and layout. In order not to get disheartened when things go wrong (as they always do!) you would do better starting with something a good deal simpler.

Have a look at a lot of circuit diagrams; there are certain conventions in circuit layout that make it much easier for you - and others - to understand what is happening. As drawn at the moment, your diagram is extremely confusing - and I speak as someone who has been doing this kind of thing probably since before you were born! :)

Phil
 

Phil-S

Joined Dec 4, 2015
238
This project would be a lot simpler if done with a mcu ("cough" arduino) and 3 relay boards.
Agreed, but getting up to speed on latching a relay in code could take a while, but long-term, the 328P is a better bet. It would still involve transistors to drive the relays either individually or a package (ULN2004?). My vote would be for MCU, but there are always latching relays to consider.
The questioner probably starting out (on vending machines?) might do well to Google Arduino. After all, just about every commercial bit of kit from boilers and programmers to washing machines and vehicles is going to use an MCU, many being Atmel. Any basic CNC machine to do the PCB will be MCU based, so not a bad idea to to see what the possibilities are. The approach as offered by the OP is physical wiring based, the MCU approach is wired in code and a lot easier to edit.
 

PhilTilson

Joined Nov 29, 2009
131
I can't help thinking that - as is often the case! - we're over-complicating things here. The proposed circuit uses 12 transistors, around 75 resistors (I lost count!) and 15 diodes. Have a look at the circuit below. It uses 6 transistors, 9 resistors, 12 diodes and a capacitor - and, as far as I know, does exactly what is required!

To give a quick run-through, it comprises three flip-flops. On switch-on, the capacitor ensures that the bases of TR2, TR4 and TR6 are held low and thus all relays are off. This can also be achieved by pressing the Reset switch.

Pressing any of the switches connected to the bases of TR1, TR3 or TR5 will force that transistor off, driving the collector high. This will turn on the opposing transistor, pulling the collector to ground and operating that particular relay. This will also pull one of the three lines below the ground line down, thus effectively resetting the other two relays.

As far as I can see, this achieves the original purpose, with far fewer components and should make for a much simpler circuit board!

Or am I missing something?

LatchingRelays.png
 

Thread Starter

ELECTROFLUX

Joined Aug 7, 2015
38
This project would be a lot simpler if done with a mcu ("cough" arduino) and 3 relay boards.
I evaluated the use of an Arduino at first, but comparing the costs between this one and the "traditional" electronic components, i opted out for the cheaper one, cost has got a priority over time.
 

Thread Starter

ELECTROFLUX

Joined Aug 7, 2015
38
I can't help thinking that - as is often the case! - we're over-complicating things here. The proposed circuit uses 12 transistors, around 75 resistors (I lost count!) and 15 diodes. Have a look at the circuit below. It uses 6 transistors, 9 resistors, 12 diodes and a capacitor - and, as far as I know, does exactly what is required!

To give a quick run-through, it comprises three flip-flops. On switch-on, the capacitor ensures that the bases of TR2, TR4 and TR6 are held low and thus all relays are off. This can also be achieved by pressing the Reset switch.

Pressing any of the switches connected to the bases of TR1, TR3 or TR5 will force that transistor off, driving the collector high. This will turn on the opposing transistor, pulling the collector to ground and operating that particular relay. This will also pull one of the three lines below the ground line down, thus effectively resetting the other two relays.

As far as I can see, this achieves the original purpose, with far fewer components and should make for a much simpler circuit board!

Or am I missing something?

View attachment 115577
Many thanks for the much more simple design Phil Tilson, if it works, will be a massive shortcut to the original one, however, as i will be using a single layer pcb, some 0 Ohms resistors will need to be added, as also the leds that seems to be missing here.
I will give it a try on a breadboard to test it, what's the value of the cap you have used?
 

PhilTilson

Joined Nov 29, 2009
131
Many thanks for the much more simple design Phil Tilson, if it works, will be a massive shortcut to the original one, however, as i will be using a single layer pcb, some 0 Ohms resistors will need to be added, as also the leds that seems to be missing here.
I will give it a try on a breadboard to test it, what's the value of the cap you have used?
One quick question - are you intending to use surface-mount devices or conventional components? This will make a big difference to how you design your PCB and whether there will be any need at all for 0 ohm resistors!
 

Thread Starter

ELECTROFLUX

Joined Aug 7, 2015
38
No SMD, i am going to use the old fashioned components, also, to make things even easier, i just decided to skip all the chemicals involved in the etching, and use a prototype board instead, i just placed an order online for a few of them :)
 

PhilTilson

Joined Nov 29, 2009
131
No SMD, i am going to use the old fashioned components, also, to make things even easier, i just decided to skip all the chemicals involved in the etching, and use a prototype board instead, i just placed an order online for a few of them :)
OK - in that case you can get by with just two wire links (or call them 0 ohm resistors if you like!) As for the LEDs, change the collector resistors from 10K to 470 ohm in each of the three cases. then connect your LEDs between the collector of TR1,3 and 5 and ground. The collector resistor will be your series, current-limiting resistor and the LED will illuminate when its respective relay operates. And that means you don't need double-pole relays, as one pole was used purely to turn on the LED!

The capacitor is not critical, as it's only used to tie down the base of the transistor at switch-on. Anything between 0.01 μF and 0.1 μF should be fine.

You might want to have a go at designing the PCB anyway, as a useful learning tool. I have done this already, and would be interested to see how you do it! As a tip, try following the circuit layout pretty closely, as it works very easily.
 
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