Filter Caps and SRF04

Steve Joblin

Working on my next robot project that uses a single Devantec SRF04 Sonic Ranger (purchased before the PING))) was available, otherwise, I would have supported Parallax!)... all is hooked up correctly and I am able to get readings, but they seem to fluctuate all over the place... I am using the RC Time function and the sample code from Acroname.· If I hold an object in up close, I get readings that bounce from 3" to 5"... if I hold an object further away, I get readings that bounce from 12" to 15" inches... relatively speaking, my wiring and program does "work", but I was wondering if the readings should keep jumping around like they do... naturally, I am thinking that there must be noise somewhere, so filter caps seem to be a good thought, but how do I select the correct values... there was just a good article in N&V about bypass caps, but it didn't give recommendations as to what values to use... any thought on "good standard practice"?

sniper1259

Steve, try this, (read it worked for me, dont know if it will work for you but worth a try) 1: install a 470uf to about 1000+ uf electrolytic cap (short for capicitor and easier to type) across the two power leads dont forget to observe polarity on the cap minus to the neg( - usualy black) wire and pos(+) to the +5v wire going to the sonar unit. 2: at the same time add a .001uf ceramic disk cap at the same place and same wires. (i spliced mine into the wires right behind the connector that hooks to the device, less than 2.5 inches away from the connector, heatshrink the splices)
reason for 2 caps; the big one filters out power glitches and spikes from the power sourcs and flattens out the power surges on the incomming power, the little one gets the rf niose on the power wires going in both directions.

also install a PI filter on the data/signal wire like this

input

---

~---(1k resestor)---~

---

out
l l
l l
(c1) .001uf (c2) .001uf
l l
l l
gnd gnd

all caps should be rated min 16v but works better with 25v and above (no more than 50v needed)

give this a try, if it dosent make sense please email me and ill send a JPG drawing. cant do much with text only
email ncc1776@comcast.net

TR

Steve Joblin

Thanks for the "quick" reply [noparse]:)[/noparse] I am amazed how people can be looking so far back in the posting history! I'll give it a try and let you know how it turns out!

Thanks again!