Howto: Designing POS equipment like a Pro - Page 1
Forum section: electronics / general

author: cavac
author_rank: Contributor
timestamp: December 10, 2021, 07:29:58 pm
content: Over the last few years, i had to work with a lot of Point-of-Sales hardware, and here is what i learned from established, professional equipment manufacturers:Make sure to re-use the power connector from the previous version, but change the voltages.If you can't change the voltages, swap the pins around in your power connector without telling anyone.Make sure you use the same type of connector for different, incompatible things and place them next to each other. Nothing is more "Pro" than having Ethernet, Serial and the 24V cash drawer connector all use RJ45, placed next to each other in a place where it's hard to read the labels.Make sure to run as much of the components as possible right at the upper edge of their specs to provide the shortest service life possible.As a bonus, make your power supply voltage drift up to very high levels when the device is not connected. That way you can kill more devices if the power supply is plugged into the wall before it is plugged into the device.If forces to support PoE, roll your own version that is incompatible with any other PoE injector or switch and make sure it fries any equipment not manufactured by your company.When designing a printer, be sure to use an optical end-of-paper sensor instead of a mechanical one. The mechanical sensors are way too compatible with different paper types and are way too reliable in dirty environments like kitchens and bars.Always choose touch screens that are easy to break with long fingernails. As a bonus, choose a touch screen that requires very strong pressing in the first place, so users are more likely to use too much force.For mobile devices: Always use the most common radio band to get the best chance of outside interference. If at all possible, make it very low range to force the customer to put up base stations every 2-3 meters.Make sure the batteries of any mobile devices charge very slowly and make the battery connectors wear out quickly. Nothing pleasures the customer more that intermittend faults.Be sure that your cash register always messes up it's database if there is an unexpected power outage.Your cash register should only work with printers that have a very specific, very outdated firmware version.If you are forced to support external screens, always choose VGA and never support anything else than a 4:3 resolution.Use the 20 digit serial number of the device as the default password and put it in a place where it's impossible to read and input at the same time. As a bonus, include lowercase 'l' and uppercase 'I' in the serialnumber.

author: daqq
author_rank: Super Contributor
timestamp: December 10, 2021, 07:39:11 pm
content: Not limited to PoS stuff:When in doubt, use a proprietary, ideally fully custom connector.

author: Sal Ammoniac
author_rank: Super Contributor
timestamp: December 10, 2021, 07:52:10 pm
content: Damn, I'm disappointed! I thought I was going to get a lesson in how to design piece of shit equipment like a pro.

author: cavac
author_rank: Contributor
timestamp: December 10, 2021, 07:57:51 pm
content: Quote from: daqq on December 10, 2021, 07:39:11 pmFor added fun, use a parts number that matches a very common electronics part or spec. Let the user have fun googling the "555 connector" or the "RS485 video cable".

author: SeanB
author_rank: Super Contributor
timestamp: December 10, 2021, 08:12:57 pm
content: You forgot that your install media is use once only, and that to reinstall you need to order a new set of media from the supplier, who will send you a nice new to you set of 3.5in diskettes, provided you send in your old media first. They also will take 3 weeks to process the return, before sending you the wrong set of diskettes, or where disk 17 of 33 is faulty, and will not read properly.Also be sure to include a hardware dongle, which absolutely has to be connected to a proper Centronics standard parallel port, which has to be the type with open collector outputs, and with a 5V termination supply, and has to be LPT1 as well, at the standard XT base address. The dongle will not work reliably with any sort of multi IO parallel port, and definitely not with any EPP port, but strangely enough will work at least the first time you use it, but will randomly fail afterwards, and brick the dongle.Otherwise use a serial port, but have an external serial to RS485 converter box, powered by a cable led out through a hole in the PC case, and with thin wire connected to a socket, attached to the 12V power supply rail. As a bonus the software will only work with a genuine 16450 UART chip, as it uses features not actually used on the original PC, and thus not implemented on the later ASIC versions, and definitely will not work with the 16550 or any on chipset emulations.

author: coppercone2
author_rank: Super Contributor
timestamp: December 13, 2021, 09:02:11 am
content: I almost dont want to give ideas here

author: nfmax
author_rank: Super Contributor
timestamp: December 13, 2021, 10:47:08 am
content: Always make sure that the clips retaining the battery cover are too strong to be opened with a fingernail, but weak enough to break when levered open with a screwdriver

author: PaulAm
author_rank: Frequent Contributor
timestamp: December 13, 2021, 06:18:43 pm
content: Haha, that brought back unpleasant memories. I had to support a POS system for a while (and to make matters worse, it was at a country club)

author: Kim Christensen
author_rank: Super Contributor
timestamp: December 13, 2021, 07:51:09 pm
content: QuoteWell, the Op did describe how to make POS POS equipment like a Pro

author: asmi
author_rank: Super Contributor
timestamp: December 13, 2021, 08:19:55 pm
content: I would add one more thing - only ever test your device at 25°C, but tell your marketing team that it can work over industrial range (0-105°C). This way you get two more failure modes for the price of one - condensation at lower temps, and overheating at high temperatures. And both modes can be easily blamed on a user (water spill for lower temps and over-insulating for high temps) with basically no way for the user to prove innocence.

author: Someone
author_rank: Super Contributor
timestamp: December 13, 2021, 10:43:08 pm
content: Quote from: asmi on December 13, 2021, 08:19:55 pmEnsure manual includes description of mandatory "ventilation" requirements, requiring open air for at least 30cm (1 foot) in all directions around the product.

author: asmi
author_rank: Super Contributor
timestamp: December 14, 2021, 12:06:46 am
content: Quote from: Someone on December 13, 2021, 10:43:08 pmThese days you might as well place poems into your manual, because nobody reads them anyway.

author: graybeard
author_rank: Frequent Contributor
timestamp: December 14, 2021, 12:56:24 am
content: I had a different definition in mind for POS than the one you are using.

author: gnavigator1007
author_rank: Unknown
timestamp: December 14, 2021, 12:58:43 am
content: Quote from: Someone on December 13, 2021, 10:43:08 pmI had the joy of repairing some POS equipment from a pizza shop and several other restaurants where my wife worked years ago. Absolutely amazing how flour gets in the air and everywhere. There was so much buildup inside everything. My favorite was the time they asked me to have a look at a printer that had fallen into a huge vat of sauce. Nobody in the kitchen noticed until someone went back to hand modify a ticket that had been sent back and it couldn't be found. I knew I was not going to be fixing that one, but it was hilarious taking it apart and showing them the microscope pics of how trashed the thing was. Pretty nasty corrosion on the pcb and many components in need of replacement, but holy hell the mechanical havoc from the combination of old flour residue and dried tomato based sauce! There was simply no way it was worth it to spend any more time than just to have a laugh