I think some holes would look better than having spacers - and it is a no-cost solution to the problem as well....
Have you planned to cut off the connector from the cable from the PSU and then solder the wires into the holes on the boards where the connector normally would be? If you put the connector on the back of the board the connections would be reversed.....
I'm not completely convinced that purple colored boards with ENIG could be considered a "downside". They look really amazing.
But being 10 times as expensive as the Seeed boards I'm not so sure that it's worth the price. Maybe for one very special board to showcase in a SOB enclosure....
$2.49 is actually only $1.25 since I was able to fit two boards on a 10x10cm pcb :-)
I've used taobaofocus.com both when I was living in Dubai as well as here in Malaysia. They are trustworthy and I got a partial refund once for parts that got damaged due to bad repacking in their facility. They deliver to most parts of the world including USA.
Currently I'm using 65daigou.com who specializes in deliveries to Malaysia and Singapore, being a VVIP level customer I only pay 4% in agent fees instead of their regular 8% :-)
That good advice - don't ever buy microcontrollers or any other hi-value ICs there. I'm sure that many of them would be fakes or factory rejects. I did purchase 1000 pcs 74HC595 once before and I got lucky, they were the real thing - but parts with a price of 10 cents aren't worth faking.
A full reel of SMD resistors or jellybean caps for $4-$7 is probably also rather hard to fake at a profit. And for that price I'm willing to take the risk. :-)
I stay away from shops with low ratings and no sales. And if they say 100000 or 1000000 "in stock" I avoid them as well.
The minimum purchase quantity can be a bit tricky to spot. But often those parts are low value parts and I want a lot of them anyways. Like the 0.02 yuan tactile switches. There had a min quantity of 2000 - not a big deal 0.02 yuan times 2000 is only $6.50.
Local shops are nice when you need a few parts right *now*, but they tend to be rather expensive. If you need a dozen or so of the parts it might be better to purchase from one of the regular major suppliers like Digikey, Mouser or Element14/Farnell, they have usually cheap overnight shipping and somewhat better prices than one of your local smaller shops.
Then there's eBay where you can find some really good deals, especially if you buy in (small) bulk quantities like 100 leds or 100 micro-usb connectors. Of course you'll be hit with a 14-20 days delivery time unless you are in the same country as the seller - usually China or USA.
But if you want really low prices on parts in bulk (or even small) quantities you should have a look at TaoBao.com. They are like a Chinese eBay where you can find electronic parts (and almost anything else) for prices that will amaze you. The site is in Chinese only, but if you're using Chrome it will automagically translate the pages to a very strange, but somewhat understandable, English. "Item" is translated to "Baby" so the search box says "Looking for what baby?" :-)
The shopkeepers normally don't ship overseas and only accepts local payment, so you need to use an agent to make your purchases. You add the url's of the items you want to purchase at the agents website. You'll then pay the agent by credit card, bank transfer or paypal and they will order all your items and collect & repack them to a single box in a warehouse in China. Then they tell you how much to pay for the shipping to you plus their agent fee (varies between 4 and 15% of the total purchase values). Once you have made this second payment they will ship the box from the warehouse to you. Usually they have rather good discounts on the standard EMS/DHL/Fedex rates.
They also usually remove all invoices and other information with prices and then put a low value on the goods in order to reduce the risk of having to pay customs & taxes in your country.
These are some of the parts that I've just bought from TaoBao. With prices like this it's easy to order a few hundred, or in case of the switches a few thousands, of them to have a small stock at home in your lab.
$0.50 100 pcs of 6x6 mm tactile switches $0.11 SMD 16 Mhz crystal (small 5x3mm, not big HC-49) $1.60 OLED display 0.96" 96x64 pixels $0.03 Piezo beeper/transducer encapsulated & wire-leads $0.07 IR 38Khz Receiver module $1.10 LiPo battery 3.7volt 240 mAh $3.45 Full reel of 5000 pcs 0805 resistors
Try matching these prices at Digikey or even eBay... :-)
One thing that I didn't buy was this 40w Laser Cutter/Engraver. For $283 it's a steal even if the quality might be shitty. Unfortunately the shipping costs would most likely be another $283 :-) Link to laser cutter
Alea iacta est. (The die is cast) I've just sent the gerbers to Seeed for this and 9 other boards.
Sure, I'll do a writeup with some screenshots of how to do this and also how to do the reverse labels I have on the top. Tomorrow I'll have a 5 hour bus ride back from Singapore Maker Faire so it might be a good way to pass the time...
Mick: Yes, it's really strange what's becoming popular or not. For instance a pcb with a connector and 5 banana jacks is a hit (don't get me wrong here, it is a nice product but I didn't expect it to be popular) and there still are free Part Ninja boards left - strange..
SMD soldering isn't that hard. If you feel confident soldering regular thru hole parts that starting with a small kit with maybe one 8 pin soic and a few 0805 discretes should not be a problem as long as you have a resonably narrow tip on your soldering iron and a solder that is not wider than 0.8 mm. There must be some nice and simple SMD training kits out there...
All parts for the Visulizer are available as standard non-SMD versions as well. The microcontroller is a ATmega8 and the three other chips are 74HC4051 analog multiplexers. The eagle files are available at https://github.com/SmallRoomLabs/Visulizer I haven't done any firmware for it yet, I'll do that when I get the PCBs.
Arup: Ah, that looks nice. Considering the width of your copper tracks it looks like the silk is partly not wider than 4-5 mils. It turned out really good. No dithered shadings though on your board, but it seems promising for my board then.
Are you doing the same as me? - Routing the backside of the board in the Eagle TOP-layer so Seeed will put their serial numbers there and not screw up your visible front side of the board?
arakis That is the bottom of the board, all smd parts are placed on the top. (The leds would be dammed hard to see otherwise :-) )
MickM: Well... According to the "capabilities sheet" from SeeedStudio they claim to be capable of a Minimum Silkscreen Width of 6 mil. [attachment=1]
So I'll try that first. If it fails it's no big deal since it's of the back side of the board anyways and then I try with a 8 mil pixel size next time. [attachment=0]
I'll probably not sell the boards as some kind of regular product, I only do them for my own amusement and the joy of routing the PCBs. :-) I probably solder up a few of them and give to local friends. I don't have a proper production line at home and having SeeedStudio do the manufacturing and fulfilment for a small batch would probably cost at least $1000 upfront and the boards might not be so popular....
Maybe doing some kind of preorder system for all my different designs to get a hint of their popularity would be a good idea...
This is the 3d-rendered front side and a screenshot of the output from WebGerber of the back side (two of them fits on a 10x10cm seeed board so I did a step&repeat). I ran a Floyd-Steinberg filter of a gif scaled to give a 6 mil pixel size and imported that onto the bPlace silk layer of the board.
Do you think it will turn out as nice as in the screenshot or will it just be a messy blur of f*cked up pixels?
[attachment=0] [attachment=1]
(The visulizer is a shield displaying the status (hi/lo/hiz) of all pins of an Arduino)
Considering that low cost was one of the basic requirements I suspect that the cost for properly wiring up 200 cat5/6 cables, getting POE switches with 200 portd in total, plus the cost of magnetics and poe-endpoints on all the units would exceed the budget by an order of magnitude... :-)
RS-485 would most likely be a good choice here. The limitation of max 32 units on the bus is very old, today many transceivers is only presenting 1/8 unit load on the bus so you can have up to 256 units.
The easiest way of having a "backchannel" would be a polling scheme. This particular application is not timing critical so the master could actually ask each slave device in turn if they have something to say. If the slave has something to send if would sent it when polled, otherwise it would either send a "null-message" to the master or just ignore the poll and let the master timeout after a few milliseconds.
I'll try it again. I still have a unopened old tub of DX paste...
I just realized that Element14 has made a "slight" increase of price of the paste I'm using. The last syringe I bought in February for $25, the price now is $74...
Yes, that is probably true using a commercial cutting service. If you do it yourself on your own (or a hackerspace) laser the cutting costs should only be like 10 cent per hour. A crappy tube lasts 3000 hours and costs about $300.
