[GreenKeys] Powering a Model 15 currentl loop from a 5VDC 250mA power supply - theory

[Gerry Block]

If anybody wants some solder paste I can give them some.

The easy way to solder fine pitch parts with a soldering iron is:

Place the part, tack solder the two corner leads, or use some instant
adhesive to hold the part.

Flood the leads with liquid flux

Drag a well tinned soldering iron across all the leads.  They will solder
themselves without shorting.  

Really!

Gerry
Ad6MC

-----Original Message-----
From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of ldesoto at comcast.net
Sent: Thursday, May 07, 2009 2:22 PM
To: greenkeys at mailman.qth.net
Subject: Re: [GreenKeys] Powering a Model 15 currentl loop from a 5VDC 250mA
power supply - theory



As long as you stick to 0805 parts and larger, it isn't hard to build SM
projects by hand.  Even 0603 parts aren't that bad.  I've built plenty of
stuff by hand using a microscope and a fine tipped iron.    The smallest
parts I've ever done by hand are 16-pin resistor packs with 0.5 mm pitch. 
The whole chip is only 4 mm long by 1.5 mm wide and they were a real pain to
do. 



One really nice way to make things is to have a solder stencil made and use
solder paste.  The only real problem is the solder paste is expensive and
has a finite shelf life.  The stencils can be made from your Gerber's and is
about $100 or so.  You don't really need a computer controlled oven if
you're careful about things and you have a way to monitor the temperature. 
Some of the stencil manufacturers will give you a telltale that you put on
the board where you can see it.  When it melts, your board is done. 



I like the stencils but they're bit on the pricey side for one-offs.  If
you're making a small 5 to 10 unit prototype run, they're well worth the
price. 



Larry 






----- Original Message ----- 
From: "John Nagle" <nagle at animats.com> 
To: greenkeys at mailman.qth.net 
Sent: Thursday, May 7, 2009 8:36:39 AM GMT -08:00 US/Canada Pacific 
Subject: Re: [GreenKeys] Powering a Model 15 currentl loop from a 5VDC 250mA
power supply - theory 

W2HX wrote: 
> How many devices in series do you think your model could handle? 
> Just curious 
> 
> 73 Eugene W2HX 

    One.  It has to be matched to the load.  It's possible to 
build ones for other loads, of course.  You'd need to increase 
C2 and change out the LT3484-1 for a LT-3484-0, which has 
a higher current limit.   You'd have to adjust R4 for a higher 
holding voltage (probably double it), and increase V1 to maybe 7V or so. 
If you want automatic load matching, that costs extra. 

    My goal was to run a Teletype from a USB laptop without much 
extra gear.  Multiple machines would go on multiple USB ports. 

    Does anybody on here build surface mount, with the little 
computer-controlled toaster oven? 

                                John Nagle 
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