---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Thu 03/26/26: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 04:05 PM - Re: Fuel System Manager (Eric Page) ________________________________ Message 1 _____________________________________ Time: 04:05:12 PM PST US Subject: AeroElectric-List: Re: Fuel System Manager From: "Eric Page" Project update: Circuit boards and components for Pete's low fuel warning module arrived and I built up a prototype. It behaved strangely when powered with 14V and didn't work at all when powered with 28V. Not very helpful in a 28V aircraft! I discovered a couple of design errors: 1) The pads for the 12V voltage regulator had the input and output pins swapped, resulting in ~26V where there should have been 12V. This exceeded the 18V max for the SA555P timer IC, causing it to behave erratically. Miraculously, it survived the abuse. 2) The unused input pins for the second comparator in the LM2903P were tied directly to ground. This was changed to 10k and 10M pull-down resistors, per Texas Instruments Application Report SNOAA35B, page 13: https://tinyurl.com/bdfvewje+ With the first problem fixed by rotating the voltage regulator 180 degrees, the module works as expected: when the LO_SNSR input has 28V removed so it's open circuit, there's a delay of 20 seconds, after which the EFIS_ALM output pulls low and the LED+ output begins to oscillate. Re-applying 28V to LO_SNSR resets the module. I've updated the schematic (attached to this post) and PCB layout. New boards and components are on the way. I'll report again when I have the new board assembled and tested. Read this topic online here: http://forums.matronics.com/viewtopic.php?p=516927#516927 Attachments: http://forums.matronics.com//files/low_fuel_warning_module_rev_c_667.pdf ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.