Is This a Sensible Way to Wire and Test My Sensors? (Multiple Perf Boards) - Page 1
Forum section: electronics / beginners

author: Potomac
author_rank: Regular Contributor
timestamp: May 14, 2016, 09:26:28 am
content: Hi all.I would appreciate some general guidance here.I am wondering if the way I have layed my project out below is a weird way to do things? Is there a better way to do this?(See picture attached below)It has certainly been time consuming, and as a beginner, I'm wondering if the way I arranged the "rails" is correct? I did test for connectivity with the buzzer on my multimeter, and things seemed to be in order for each individual board. I laid things out this way in order to ensure good electrical connections and to be able to power all the LED's on one set of rails, and all the phototransistors on the opposite rails. The breadboard was just too frustrating to deal with. (Having things moving around all the time while I take analog to digital readings)In the picture below, you'll see a series of perf boards layed out in a vertical orientation. They each have 2 circuits containing Omron EE-SX1140 sensors soldered to them, which I'm feeding into the analog inputs of my Sparkfun Arduino Pro Mini (8 analog inputs).The EE-SX1140 is composed an IR LED and a IR phototransistor (a photodiode connected to a BJT).It normally is used to detect whether or not something is present between the slot. A binary "yes" or "no" is registered. However, I'm repurposing it slightly to give me an analog readout. With my circuit when an semi transparent item is placed in between the slot, the phototransistor outputs a voltage proportionate to the amount of light transmitted across the slot.I eventually want to use my Sparkfun Arduino Pro Mini to test how consistent the readings are for my translucent plastic reference item of choice. I'm looking to obtain some fairly comprehensive data to prove that these sensors are worth using.I can only fit 2 sensor circuits comfortably on each small perf board. I thought about buying a long narrow perfboard from Digikey, but they cost over $40, and I kind of like the "modularity" of this systemThe perf boards are attached to a piece of lasercut plexiglass using aluminum hex standoffs.My specific question was if it's wise to have these modular perf boards and if you see any flaws with the "rails" layout? I actually had some trouble obtaining readings late tonight and plan on re-trying yesterday. May have something to do with the way I arranged the "common ground" wires.Here's the sensor datasheet f anyone is just curious.https://www.components.omron.com/components/web/pdflib.nsf/0/1BAE6FC8D18BE5D585257201007DD4D4/$file/EE_SX1140_1010.pdf

author: Ian.M
author_rank: Super Contributor
timestamp: May 14, 2016, 10:19:45 am
content: No. Mount the sensors where they need to be physically and wire each back to ONE matrix board that carries all the LED and output resistors, and has a 4 or 5 pin 0.1" pitch header for each sensor all in a row. Use shells and female contacts on the board end of each sensor cable. At the sensor end, if the plastic shell stands up to normal soldering temperatures, simply solder a wire to each pin and sleeve withHellermanor heatshrink sleeving. If it distorts when you solder it, use an offcut of matrix board to stabilise its pins and provide more pad area for the wires, or even to attach a 4 way rightangle header so you can make both ends pluggable.Finally, leave enough slack in all the cables so you can dress them into a neat wiring loom and secure them to your baseboard with cable clips. Hand-lacing looms is nearly a lost art, spiral wrap or expanding braid is fugly to work with when you need to add/remove wires, cable ties are just plain ugly and also wasteful if you are frequently modifying the loom and split corrugated tubing is somewhat chunky but is the easiest to modify. I'm a cheapskate so will twist-tie till its finalised then replace with cable ties, or hand-lace it if its gotta be neat. The only reason *NOT* to loom wires is if they carry sensitive low-level signals that *MUST* be wired direct point to point to reduce noise pickup.

author: Potomac
author_rank: Regular Contributor
timestamp: May 14, 2016, 11:48:56 am
content: Not sure exactly how to draw what you described. I started doing it a little bit in Paint but was unsure if I was drawing what you were communicating.(To get the proper spacing I want on the sensors and be able to fit them on one board, I'd need a pricey board from Digikey. Something like this. Just obscene pricing for fiberglass with plated through hole pads.http://www.digikey.com/product-detail/en/vector-electronics/8010/V1117-ND/146824)To answer your question about noise, I am definitely trying to avoid that. The manufacturing tolerance of the sensors already contributes to variation when using identical reference standards for the simultaneous measurements. (This is for a lab application)Not sure if braiding the cables is going to be good for that. Trying to avoid cables flapping in the wind in general too.

author: Ian.M
author_rank: Super Contributor
timestamp: May 14, 2016, 12:20:58 pm
content: Who said anything about putting all the sensors on one board? I said mount each one individually to your perspex baseboard, either hard-wired direct to its cable or on a mini-board to connect to its cable. One cable per sensor, no spliced grounds or power wires.If you put the Arduino Mini on the same board as the headers for the sensors and their LED and load resistors, you'll have a neat one board solution.