September 20, 2013

Project: New Old Stock Electronic Lock Kit

The return of cooler fall weather and rain prompted a trip to the workshop for a little solder smoke aroma therapy.  It had been a long hot summer and sadly the workshop was idle during most of it.

The first thing we decided to do was to perform a little clutter management.  All of the horizontal surfaces had become parking places for various tools and detritus.  We needed to reclaim some workspace and create a safe work environment.

During the cleanup we discovered a long-forgotten kit in a polybag.  It was a vintage electronic lock kit perhaps from the 80's that we had purchased for a couple of dollars via eBay.  The kit was rather basic having only a schematic, a bag of parts, and PCB without any markings.  No step-by-step instructions were provided.  A little mystery to add to the fun!

The purpose of the device once built is to activate a double-pole-single-throw switching relay when the user enters the correct sequence of four push buttons.  A reset button returns the relay to its normal setting.  The kit requires a 12v input.

We had a spare unused enclosure on the shelf that looked like it would fit the kit perfectly.

NJ2X Electronic Lock - Finished Build

Step 1: Review all the components and determine the target location on the PCB.
  • This went fairly well.  The only tricky part was to make sure the orientation of the transistor, capacitor, and IC's was correct.  The schematic helped.
Step 2: Solder in the jumpers.
  • Some of the jumpers needed to located underneath components.  This little insight helped us keep the build looking nice and neat.
Step 3: Solder all the components.
  • Pay careful attention to the IC's.  There were three IC's with the same number of pins though 2 different part numbers.  An easy mistake would have been to misplace the IC's.
  • We used a generous amount of flux on the parts and board due to obvious oxidization and a little corrosion.  The flux helped greatly with cleaning and promoting good soldering.
Step 4: Clean up the solder flux.
  • Using cotton swabs and alcohol quickly cleaned the PCB and components of flux residue.
  • This step keeps the build looking nice and neat.
Step 5: Mount the pushbuttons.
  • We used a drill press and 5/8 inch drill bit to prepare the faceplate.
Step 6: Solder wires for power, push buttons, and relay switching
  • We used Anderson PowerPole connectors (of course) for the 12v power input with a bit of shrink tubing for added strain relief.
  • We added three wires to the relay switch.  These can be used for switching applications.
  • We used heavier gage wire than what the kit was drilled for.  This was quickly remedied with a Dremel tool and suitable bit.
Step 7: Power up the circuit and test it
  • Test 1: Activate the relay (no load) by entering the correct lock sequence.  SUCCESS
  • Test 2: The relay is not activated (no load) by entering an incorrect lock sequence.  SUCCESS
  • Test 3: Add a load (audio continuity tester) to the switch inputs and repeat tests #1 and #2.  SUCCESS
  • Test 4: Repeat tests #3 using the other pole of the relay. SUCCESS
This old kit was a great way to kick off the kit building season.  The solder smoke aroma therapy worked as it should resulting in a sense of satisfaction having build a neat little electronic gadget.

On the application side, we still haven't decided what we need to turn on or off with this device yet.  You never know when inspiration will strike.  When it does, we will put this device to good use.

Good DX and 73, NJ2X

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© Michael W. Maher and NJ2X.COM, 2013. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Michael W. Maher and NJ2X.COM with appropriate and specific direction to the original content.