On Wednesday, April 29, 2015 at 12:06 PM, owfs-developers-requ...@lists.sourceforge.net wrote: From: Paul W Panish <ppan...@panishnet.com> Subject: [Owfs-developers] Temperature sensitive bus timing using DS18B20
> My problem is that there seems to be a strong temperature dependency for > bus read/write errors caused by the DS18B20 sensors. I?ve replaced the > sensors a few times with devices purchased at different times and from > different vendors to rule out random bad devices. > > I?m using a polling loop to read the DS18B20?s and PIO inputs at 5 > second intervals with a conversion resolution of 10 bits > (temperature10). When the system is cold (<140 degrees F) it can go > forever (months) with no errors indicated in any device access. However, > when I fire the boiler I start seeing access errors (file not found) as > the boiler temperature rises above roughly 150 degrees. The error rate > increases as temperatures rise to a maximum level of about 185 degrees > at which point they are quite severe. I would say there is no such problem with the 18B20 itself. I've had ten of them strung around my house since 2002, from solar panels on the roof to the wood boiler on the lowest level, easily 100 feet of CAT5 in a single bus with the computer connected in the middle. The solar and wood sources regularly take them to 160F and fairly often beyond 185F, occasionally over 200F, and (unless I've done something transient to mess up the communication) I see exactly zero errors. These are not on OWFS, they are directly wired to an ancient microcontroller with custom software, which reports and logs _every_ failed or anomalous reading - once per second to 12 bits, year after year. Since I added the active pullup and pulldown interface, and Schottky diodes and TVS protection at each end of the bus, they have been absolutely bulletproof. I'm here because I'd like to duplicate that reliability using modern hardware with the convenience of swapping a USB plug instead of tinkering with my jungle of discrete wiring. My first experiment was to hang a couple of 18B20s off the w1 interface of my BBB with OWFS, and while they are read reliably, the readings are consistently about 4F and 8F higher than the same chips when connected to the old controller (where they match my thermocouple thermometer exactly). So I'm watching for ideas on which USB interface to try... Hobbyboards seems to be well recommended, but this kind of report makes me worry. Are you using their USB interface to reach your 18B20s? I guess you didn't actually say that... Loren ------------------------------------------------------------------------------ One dashboard for servers and applications across Physical-Virtual-Cloud Widest out-of-the-box monitoring support with 50+ applications Performance metrics, stats and reports that give you Actionable Insights Deep dive visibility with transaction tracing using APM Insight. http://ad.doubleclick.net/ddm/clk/290420510;117567292;y _______________________________________________ Owfs-developers mailing list Owfs-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/owfs-developers
