Today's Message Index:
----------------------
1. 04:05 PM - Re: Fuel System Manager (Eric Page)
Message 1
| INDEX | Back to Main INDEX |
| NEXT | Skip to NEXT Message |
| LIST | Reply to LIST Regarding this Message |
| SENDER | Reply to SENDER Regarding this Message |
|
| Subject: | Re: Fuel System Manager |
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
These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.
-- Please support this service by making your Contribution today! --
|