From: Bdale Garbee Date: Mon, 29 Apr 2013 16:23:53 +0000 (-0600) Subject: first cut at a document on using a separate pyro battery, no pix yet X-Git-Url: https://git.gag.com/?a=commitdiff_plain;h=3d836ff7c0643c81d7c145819c002eb1d3126100;p=web%2Faltusmetrum first cut at a document on using a separate pyro battery, no pix yet --- diff --git a/Documents/SeparatePyroBattery/index.mdwn b/Documents/SeparatePyroBattery/index.mdwn new file mode 100644 index 0000000..eb01f5c --- /dev/null +++ b/Documents/SeparatePyroBattery/index.mdwn @@ -0,0 +1,91 @@ +[[!meta title="SeparatePyroBattery"]] + +# Using a Separate Pyro Battery with Altus Metrum Flight Computers # + +As we have discussed +[elsewhere](http://gag.com/bdale/blog/posts/Batteries_and_Pyro_Circuits.html), +the most reliable solution for pyro control circuits in large and complex +rocket projects is to use a separate battery to provide the current +used for actually igniting the charges from the one used to power the +electronics. This document explains how to do this with various +[Altus Metrum](http://altusmetrum.org) flight computer models. + +## Pyro Circuit Background ## + +All Altus Metrum flight computers use low-side FET switches to control pyro +events. What this means is that the pyro circuit provides the equivalent of +a switch to ground on one pin of each pyro circuit, and a source of power on +the other. The continuity sense circuitry is on the switch side of the pyro +terminals, and was designed to cope with any pyro voltage through nominal +12 volts (15 volts DC maximum). Using a separate pyro battery is therefore +as simple as just ignoring the terminal that provides a source of voltage and +only connecting the side that provides the switch to ground. + +The negative lead of your pyro battery needs to be connected to ground on +the flight computer. The plating around the mounting screw holes is one +good place to find ground. The negative terminal of the LiPo battery +connector is also grounded. And on TeleMetrum boards there's an explicit +ground connection hole you can solder a wire to. + +The positive lead of your pyro battery needs to connect to one side of each +e-match, with the other side of the match connecting to the appropriate +pyro terminal on the flight computer. This obviously means you need to make +connections off-board. Whether you choose to do this with a screw terminal +strip, crimp connectors, or by soldering wires together is of course entirely +up to you! + +## TeleMetrum ## + +Early [TeleMetrum](http://altusmetrum.org/TeleMetrum) boards had an +unpopulated connector footprint on the board +for a separate pyro battery, but due to a wiring error in the design of the +board, that connector was never useful. Just ignore it. + +If you look at the bottom of the board where all the surface-mounted components +are, on the end where the pyro screw terminals are located, you can see a +fat trace connecting three of the screw terminals together. This is the +source of pyro power, which comes from the LiPo battery through the power +switch and then to one side of each pyro channel. The pins that trace +connects are therefore the ones you want to ignore. The others are the +switches to ground. + +Here's a photo of the pyro end of a TeleMetrum board augmented to show what +to connect where: + + + +## TeleMini ## + +Wiring a [TeleMini](http://altusmetrum.org/TeleMini) board for use with a +separate pyro battery works the same way. + +If you look at the bottom of the board where all the surface-mounted components +are, on the end where the pyro screw terminals are located, you can see a fat +trace connecting two of the screws. This is the +source of pyro power, which comes from the LiPo battery through the power +switch and then to one side of each pyro channel. The pins that trace +connects are therefore the ones you want to ignore. The others are the +switches to ground. + +Here's a photo of the pyro end of a TeleMini board augmented to show what +to connect where: + + + +## TeleMega ## + +Because [TeleMega](http://altusmetrum.org/TeleMega) was designed to +be especially well suited for use in large +and complex projects, it includes extra screw terminals on board to make use +of a separate pyro battery easy. In fact, use of a TeleMega with only one +battery requires putting a jumper between two adjacent screw terminals to +connect the main LiPo battery to the pyro power rail. + +To use a separate pyro battery, just leave out the jumper and connect the +pyro battery to the two adjacent screw terminals marked 'gnd' and 'pyro', +using the 'gnd' terminal for the negative battery lead and the 'pyro' +terminal for the positive side. + +Here's a photo showing the a TeleMega board wired this way: + + diff --git a/Documents/index.mdwn b/Documents/index.mdwn index 44b9e0f..8f0238e 100644 --- a/Documents/index.mdwn +++ b/Documents/index.mdwn @@ -12,6 +12,7 @@ think before you act! ## How-To Documents ## * [Remove the protection circuit board from a LiPo battery](./FixBattery) + * [Use a separate pyro battery](./SeparatePyroBattery) ## Collected References ##