#garfield Logs

Jan 26 2015

01:01 rue_house hey
01:14 katsmeow-afk hmm?
01:15 katsmeow-afk okgnite
15:58 katsmeow-afk http://www.technewsworld.com/story/81634.html
19:02 Tom_itx yay! at least it's in the states now
19:06 katsmeow-afk what is?
19:07 Tom_itx my china stuff
19:08 Tom_L http://www.ebay.com/itm/161440667181
19:10 katsmeow-afk oooo
19:10 Tom_itx http://www.homanndesigns.com/store/index.php?main_page=product_info&cPath=15&products_id=30&zenid=cc1252fbd4s9opftaavu2av841
19:10 Tom_itx same thing
19:11 katsmeow-afk ouch
19:12 rue_house I was in the jail almost all day
19:13 rue_house installing data lines
19:13 rue_house lots of concrete
19:13 rue_house and a bit of EMT pipework
19:14 katsmeow-afk emy in a jail? i'd thought they'd make youuse waterpipe, so peole canot rip it apart
19:14 katsmeow-afk arg
19:14 katsmeow-afk shift the keybd a li bit, can't find it any more
19:17 katsmeow-afk i installed aubs mouse on the laptop, but it won't let me click and drag hi-light
21:35 rue_shop3 tiny26, 74ls166, 75ls595
22:08 Tom_itx inmates try to hitch a ride home with you?
22:10 rue_house no, they were all too drunk to work that out
22:39 Tom_itx 4.7v zenner work for a crowbar for a 5v circuit or should it be higher?
22:39 Tom_itx 4.7k in series
22:49 rue_house higher
23:01 katsmeow-afk neverwork just try it with a variabe psu
23:02 katsmeow-afk 1) it won't simulate dropping a crowbar across your 5v buss
23:02 katsmeow-afk 2) zeners are very "soft", it will be off from temperature and current
23:03 katsmeow-afk sounds like you are building a clamp, not a crowbar, and i doubt your zever will survive getting hit with your 24v supply
23:05 katsmeow-afk and if it does survive even a few ms, it won' clamp down to 5v, and after it burns up it cerainly won't
23:05 katsmeow-afk https://en.wikipedia.org/wiki/Crowbar_%28circuit%29 <<== has a circuit, there's various ways to make it happen
23:07 katsmeow-afk The LM431 is a 3-terminal adjustable shunt regulator with
23:07 katsmeow-afk guaranteed temperature stability over the entire temperature
23:07 katsmeow-afk range of operation.
23:15 katsmeow-afk ...
23:27 rue_house but once a zener fails it tends to become a dead short
23:28 rue_house kat is right tho, use a circuit that dosn't destroy itself in the act of protecting your system
23:28 katsmeow-afk most zeners will burn open while discharging the 24v main caps
23:29 katsmeow-afk you need heavy duty current capacity, but the pint is to blow a fuse, so heat isn't a problem, even if you need to use a stud or TO-3 shroting transistor/scr/triac/mosfet
23:31 katsmeow-afk it will take some time for the crowbar to fire, so the 5v supply shoud have enoug capacitance to absorb the short to higher voltage until the crowbar fires
23:37 katsmeow-afk a test rig would use two psu, isolation diodes for each, a recurring trigger to gate a fet/transistor to shor them together, while you watch on the scope, see if it's fast enough, check the voltage excursions, etc
23:39 tsmeow-afk keeps playing solit
23:51 e_bed tries to work out symptoms of depres