MS20 and relay problem solved

dharter

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I had used a 12V relay that I bought from Jameco.  It had PC leads.  I had mounted it in an ammo can outside of the MS20 sensor.  Last time I had mounted one inside, I had a hard time getting the ms20 case  to close.  The stress on the PC leads of the relay caused the connection to become intermittent.  I decided to replace it with a 12 V realy that had solder lugs.  I went to Radio Shack and bought their 12VDC DPDT Plug-in-relay (275-218C)  The ms20 would trip but the relay would not.  It turns out that the ms20 could not sink enough current to turn on the relay.  This realy is rated at 12Vdc and 75mA or 160 Ohms.
I went back to Radio shack and bought a 1K resistor and a MPS2907 (276-2023) transistor.  I soldered one end of the resistor to the lead in the ms20 that would sink the current to turn on the relay.  I soldered the other end of the resistor to the base of the transistor. I used a clip across the leads of the transistor to prevent it from overheating during soldering. I soldered the emitter of the transistor to one of the relay contacts.  The other relay contact is connected to 12V.  The collector of the transistor is soldered to ground.  When the ms20 is triggered, it turns on the transistor inside it.  Current then flows from the 12V supply through the relay through the emitter of the external transistor, through the base of the external transistor and through the internal transistor to ground.  That base current of the external transistor turns on the external transistor.  Current now flows through the relay through the external transistor to ground.  The relay turns on and my camera now works.  The drawback is that I can now hear the relay turn on.
 

Richard Webb

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Hi dharter - I had the same problem with the MS20 last month when I tried to use a 6 Volt Relay. (NTE 6 VDC Relay @ 70 Ohms  360lmW).  The MS20 has a voltage regulator set at 5 volts, so all voltage above 5 volts is wasted. I figured that if I used a 6 volt lantern battery with the NTE 6 volt relay everything would be kool. But, the MS20 couldn't sink the 70 Ohm Relay, so I gave up on it completely. Do you think your external transistor idea would work with this 70 Ohm Relay?
 

dharter

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It looks like your relay would draw 85ma at 6 V. That is probably why it didn't work.  The ms20 could not sink that much current to turn on the  relay.  I think that the external transistor could help.  It amplifies the current from the ms20 internal transistor.  You should proabably use a diode in parallel with your relay to prevent high induced voltages when the realy turns off.  When the relay is on make sure that the resistor is not drawing more current than it is rated for.  Measure the voltage across it, square it , divide that result by the value of the resistor and you get the watts dissipated by the resistor when the relay is on.  So if your resistor is .25 W , you should not be dissipating more than that.  
   
 

KsBowhunter

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I've got 2 cams w/MS20's and Tinhorn/Welby's front end timer.

My question is: How can I get rid of the relay on the MS20 board and still trigger the timer?

The timer has a relay at the end to fire the cam, and I think that both relay's are causing to much delay between the time the PIR fires and the camera shutter trips.

Any suggestions?  :|
 

Brian

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Gentlemen,

Jameco sells  DIP relays that are totally noiseless when operating.

You can use a transistor  as an amplifier and turn this relay on with a current draw of approximately 8mA when activated.  I use a 3k resistor, a 2N3904 transistor and a dip relay from Jameco and it works great.  You're not interest that much in current draw from the contact closure to the camera just in the current needed to turn on the relay.  

The part number for the DIP relay I use is: 138430
This is a 5VDC SPST DIP relay. Contact current is .5 Amps.

Make sure the ground of the trigger is connected to the ground of the relay coil in the proper position because this relay has a built in diode.  The pin marked (-).  Connect the trigger of 5 volts from the sensor to the base of 3k resistor and the other end of the resistor to the base of the transistor.  Hook 5 volts to the Collector from the batter itself and not from the MS20 and hook the emitter to the other relay pin marked +.  This circuit should turn on the relay when the trigger is activated and it only draws about 8uA from the MS20 supply and the 8mA will come from the battery itself.

You can hook this circuit up where the relay coil is in the collector instead of the emitter but they will work the same since the collector current and the emitter current are almost matched due to the properties of this NPN transistor.  

Jameco also has other voltage/current configurations for all types of designs.


Brian
 

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