A little advice for my first circuit board? - Page 1
Forum section: electronics / beginners

author: Godulous
author_rank: Newbie
timestamp: March 30, 2013, 04:15:46 am
content: Hi guys, I've been playing with my arduino for quite some time now so I'm a little bit familiar with electronics and components, but I want to build my first stand-alone circuit board now and I'm not sure where to start. I would appreciate any advice, resources, or links to information. The purpose of the board will be very simple, it just needs to have 2 knobs that can adjust the speed of a motor and a the rate of a blinking LED. I'm not sure what the best way to achieve this would be, or what the cheapest kind of way to control it is.Appreciate any help in advanced!

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: March 30, 2013, 06:44:15 am
content: For my first board, I went from the breadboard (you were planning to prototype on a breadboard, right?) to a circuit board that had copper traces just like a breadboard. I put that into a generic plastic project box and cut holes where I needed them. I used aTeensy.I'm pretty beginner myself, but some questions do pop out: What kind of motor? Something with a voltage-based speed or something that needs more? How much power is going to the motor? I take it you want the led to blink based on the motor speed setting?

author: Godulous
author_rank: Newbie
timestamp: March 30, 2013, 07:44:32 am
content: It's just a small 3-9v DC motor, I was going to have it powered by a few AA batteries. The speed of the motor and LEDs is independent, each controlled by a potentiometer. I had something similar working through my arduino but I'm not sure how to translate something like that to a board I have to make from scratch and designed around cost effective parts (I probably want to make a few dozen of them).

author: Kremmen
author_rank: Super Contributor
timestamp: March 30, 2013, 08:15:45 am
content: Quote from: Godulous on March 30, 2013, 04:15:46 amOK, it is a fair question so i'll try to answer.You say standalone, so i assume you mean the Arduino you mentioned, is not involved? Let's make that assumption. It immediately follows that you need to design 2 circuits from scratch: a simple motor speed controller and a LED blinker. Those again divide into 2 parts: circuit design and physical build.Circuit design:-First fix the parametes of your circuit as far as you are able. Question that need answering are e.g. what kind of motor - max voltage/current/rpm/power, how precise control exactly, budget for the implementation etc. Similarly for the LED - what range of blink rates, any specs on brightness, color, things like that.-Once you have the target more or less fixed you can start aiming at it. I leave the actual design for you but the usual solutions are a simple pwm control for a DC motor and a slow oscillator of some kind for the LED. Google will be your friend, as will Digikey, Mouser, Farnell and similar vendors for parts and datasheets. Tayda and Futurlec in Asia are reasonably priced vendors although they have limited range of stock available. Some items are real cheap though and perfect for hobby/prototyping.-The "usual" workflow for electronics design is to start by designing the first approximation for a circuit. Once that is more or less done you should simulate until happy with the apparent working of the circuit. Then build a prototype and once the smoke has cleared, go back to the drawing board to find out what went wrong. Continue this cycle until the prototype works as well as it can be expected to do. At this stage a popular tool is the SPICE simulator LTSpice, available free from Linear Tech athttp://www.linear.com/designtools/software/. Do spend considerable time to learn how to use this tool. It will be invaluable in all future design efforts if you do so.Build:-Next question will be how to build the end product. In fact at this stage you have already built prototypes so the question has been at least partially answered there. However, most prototypes are built as such and don't necessarily reflect the mechanical requirements of the finished product. For the circuit part, 2 basic alternatives exist;-- use a prototyping board to hand build the actual circuits as well as to hold the components. This works for relatively simple circuits and small numbers but gets tedious quickly if there are more items to construct or they have any complexity at all. Also, modern fine pitch SMD packages are not suitable for proto board construction so you need to maintain separate versions of same components for proto and final assembly.-- the alternative is to either make the proto boards, or have them made. The advantage is that you then don't need different boards for proto and final product. The drawback is that should a proto board have errors, fixing those needs another round of board production. There is continuing debate/discussion whether it makes sense to maintain the capability to roll your own boards when shops like ITead Studiohttp://imall.iteadstudio.com/open-pcb/pcb-prototyping.htmland Seeed produce boards in small series at such low prices. This is a question only you can answer for yourself. To make boards adds a layer of complexity and work, not to mention the fact that you need a place to do the work and store the chemicals, some of which are not exactly vitamins. The upside is that you can get a board made on a couple hours notice. I do it on occasion and it is not many days since i last made a set of simple audible/visual alert boards for a project, thus avoiding a wait of 2-3 weeks.Having said that, use of the board mfg service will provide professionally produced boards with features unavailable in home cooked alternatives, like overlay print (silk), solder masking and true 2 layer (or more) designs with plated holes and proper vias.To be able to benefit from professionally manufactured boards, you need to provide the vendor with proper design info in the form of Gerber files describing your board layout in its details. These files are produced by PCB design software and i suggest you learn how to use one of those. Popular free alternatives are e.g. Eagle and KiCAD but personally i am partial to Diptrace which i feel is easily superior to either of the previously mentioned ones. There is a free version, crippled to max 300 pads/2 layers available athttp://www.diptrace.com. That would be my choice and when your needs grow there are reasonably priced upgrade paths.

author: Godulous
author_rank: Newbie
timestamp: March 30, 2013, 09:28:44 am
content: Thanks a lot for the post, it was very informative and it's given me a good place to start. To answer some of your questions:The motor is 2.5V-6V and approximately 400 mW, rpm and precision are not important as long as they can be controlled by the potentiometer.The LEDs will be blinking somewhere in the 20-1000hz range, again with precision being unimportant. I've seen videos of adjustable blinking LEDs using a 555 timer but I don't know how to figure out if that works for my frequency range. (or how to use 555 timers)Ultimately I would like for each board to be <$10, I just don't have any idea what the simplest and easiest approach to doing something like this is as I have no in depth knowledge about electronics.

author: hlavac
author_rank: Frequent Contributor
timestamp: March 30, 2013, 12:13:39 pm
content: If you want cheap PCB boards you will need to learn to make them.I get best results with ready made photosensitive PCB material,printouts on tracing paper for masks, a nice UV light made from UV LEDs for exposition, 10g of NaOH/1l of water for developer (you can buy it as a drain cleaner). I use CuCl based "infinite" etching solution that can be reused almost forever instead of the messy ferric chloride. I don't pour it down the drain, i keep using it.You can make it by mixing HCl with peroxide (both 30%, 1:1) and etching some PCBs in it. Watch out,this initial etchant is very quick!When it turns nice green you have proper CuCl based etchant.When it turns brownish it is tired and needs a bit of oxygen to refresh. A little bit of peroxide turns it back green. If it does not add a bit of HCl. Use a container with spare space as you will have more of it over timeThen of course you need a small drill with a stand for the holes.I started with cheap plastic drill stand and drill, it was kind of ok, but I later got a nicer one. This is vital equipment, I suggest you get a good one.

author: Kremmen
author_rank: Super Contributor
timestamp: March 30, 2013, 01:46:26 pm
content: You (OP) wrote earlier that you want to make a few dozen boards. That is a small production run and would be IMO best ordered from a supplier like ITead etc. Their "small batch" of max 50 5x5 cm boards is just $45 - i wouldn't bother making them at that price. And you will get a proper 2 sided board with all standard features.Since the motor is so tiny, a 555 based pwm circuit assisted with a simple transistor or FET will do fine. Google for 555 and "pwm".Likewise the LED circuit, a 555 can source and sink some 300 mA if memory serves, so you don't need anything else, the 555 will drive your LED just fine. Now for the LED there are potentially 2 adjustments, frequency and duty cycle. Both can be adjusted using a 555, but not both by one 555 at the same time. So you need a more complex solution if you want to adjust both. I could provide the circuits but where would the fun be in that? Assuredly you can find examples of both circuits in the net, as well as info on the 555. A suggestion: go towww.digikey.com, search for "LM555" and open one of the resulting items. You will find a link to the 555 datasheet. There is your first subject of study. Once you understand how the component works, you can do all kinds of stuff with it, and you will also understand the circuits you find that use it.

author: Godulous
author_rank: Newbie
timestamp: March 31, 2013, 03:40:02 am
content: Thanks for all of the information, after looking into it some more I think I'm going to try to go the 555 route as it seems simple, effective, and cheap for my purpose.