Attended ESC Boston 2012. Now called Design East.
http://east.ubmdesign.com/
http://events.ubm.com/event/1713/esc-boston-embedded-systems-conference
http://en.wikipedia.org/wiki/Embedded_Systems_Conference
http://en.wikipedia.org/wiki/Embedded_Systems_Conference#ESC_Boston
Glad to see a few of the familiar faces and ask them about new trends in the industry.
Lantronix http://www.lantronix.com/ xPico
Microchip http://www.microchip.com/ Metering and Wifi
Various systems based on ARM processors
http://en.wikipedia.org/wiki/ARM_architecture
Our mantra is "more RAM". Even if just for one sensor and minimal OS features - still want DB and security - 256M minimum.
Power over Ethernet 802.3af and 802.3at.
http://en.wikipedia.org/wiki/Power_over_Ethernet
http://www.silvertel.com/
Should give positive mention to Symmetry http://www.symmetryelectronics.com/ for hosting Lantronix, Silvertel and others.
Looked at Wurth Ethernet 802.3af magnetics with LED. http://www.we-online.com/web/en/wuerth_elektronik/start.php
Toradex - USB sensors and ARM processors. http://www.toradex.com/
Interesting talk on Internet of Things http://en.wikipedia.org/wiki/Internet_of_Things
by Micheal Anderson of PTR http://www.theptrgroup.com/
Blogged before of Google Goggles to read meters. Visited Vision Components http://www.vision-components.com/en/ and looked at their smart cameras.
Wednesday, September 19, 2012
Thursday, September 13, 2012
RS485 Rule of Thumb: N x L x kB x P < 485
RS485 rule of thumb: N x L x kB x P < 485
This is for RS485 bus architectures like those for Modbus RTU, BACnet MSTP, Johnson Controls N2 and so forth.
N x L x kB x P < 485
Where
N = the number of quarter (or less) load devices. If using older full load devices then consider each device as four devices. For example three quarter load devices plus three full load devices and two sixteenth load devices would mean N = 3 + 12 + 2.
L = the length of the line in 100m multiples. For example 1000m (1000yards) means L=10.
kB = the speed in kBaud. For example 9600 baud would be kB=10
P = The problem factor. P is a number which is usually unity when all the line characteristics are well conditioned. Double it for poor biasing. Double it for poor termination. Double it again if runs are close to motors or transformers. Double it for improper capacitance. Double it for poor twisting. Double it for ground faults like poor/weak or multiple grounding.
So a 100m line with four quarter loads running at 20kB with a couple of problems P=4 (320) is probably okay. But a 1000m line with ten quarter loads running at 10kB with P=1 (1000) is likely problematic.
[Updated 2012.09.19 by rescaling L to make the arbitrary number '485' easier to remember.]
This is for RS485 bus architectures like those for Modbus RTU, BACnet MSTP, Johnson Controls N2 and so forth.
N x L x kB x P < 485
Where
N = the number of quarter (or less) load devices. If using older full load devices then consider each device as four devices. For example three quarter load devices plus three full load devices and two sixteenth load devices would mean N = 3 + 12 + 2.
L = the length of the line in 100m multiples. For example 1000m (1000yards) means L=10.
kB = the speed in kBaud. For example 9600 baud would be kB=10
P = The problem factor. P is a number which is usually unity when all the line characteristics are well conditioned. Double it for poor biasing. Double it for poor termination. Double it again if runs are close to motors or transformers. Double it for improper capacitance. Double it for poor twisting. Double it for ground faults like poor/weak or multiple grounding.
So a 100m line with four quarter loads running at 20kB with a couple of problems P=4 (320) is probably okay. But a 1000m line with ten quarter loads running at 10kB with P=1 (1000) is likely problematic.
[Updated 2012.09.19 by rescaling L to make the arbitrary number '485' easier to remember.]
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