need to amplify ~.2V to trip a relay

[meltedeyes]

Hey all,

I'm looking for a simple circuit that will amplify a pulsing .2V to roughly 9-12V.

I think a simple op-amp will do it, but I'm not sure.

The application:
I am using an electronic dog collar to trip a latching relay when it get's too close to the transmitter (roughly 6 feet). This is going on a mobile platform so all power is going to be coming from batteries.

The dog collar operates in pulses at roughly 100Hz if memory serves. All I need the amplifier to do is provide enough voltage to trip a latching relay in a short amount of time.

Vin: .2
Vout: 9+

I've managed to dredge up enough 11 year old knowledge to build (and have tested) the rest of the circuit. I just don't remember enough for this initial part. I've spent some time reading old text books and on Google, but I'm running out of time to get this thing operational.

And no, this is not being attached to any animal.

Thanks.

 

[mneary]

How much current can you get from the 0.2V?

 

[Speakerguy]

Single, Strobed, High Speed Differential Comparator with Push-Pull Outputs - LM306 - TI Product Folder

The LM306 is a high-speed voltage comparator with differential inputs, a low-impedance high-
sink-current (100 mA) output, and two strobe inputs. This device detects low-level analog or digital signals and can drive digital logic or lamps and relays directly. Short-circuit protection and surge-current limiting is provided.

 

[meltedeyes]

How much current can you get from the 0.2V?

I'm not sure. My DMM varies between .2 and .4 volts with each pulse, and I have not been able to get an amperage reading. I am thinking that the pulse is too quick for my DMM to get good readings.

 

[meltedeyes]

Single, Strobed, High Speed Differential Comparator with Push-Pull Outputs - LM306 - TI Product Folder

Okay, If I am reading that paper correctly, if I attach the dog collar to the strobe, it should detect the small voltage and then output the difference between IN+ and IN-?

Or at any rate, a logic high on the strobe will cause the OUT to go high and trip the relay, correct?

 

[Speakerguy]

Tie both strobe inputs to +VCC, use a resistor divider to set the - input to 0.1V, input your signal to the + input. You won't be using the strobing function. This assumes a well regulated 9V supply.

 

[Mikebits]

I'm not sure. My DMM varies between .2 and .4 volts with each pulse, and I have not been able to get an amperage reading. I am thinking that the pulse is too quick for my DMM to get good readings.

So are you saying you that you determined your input to be .2v based on a DMM. If this is a pulsing signal I suspect a DMM will not give you what your input voltage really is. You need to use a scope or determine the signal from the design.

 

[mneary]

Maybe we can guess using another approach. What is the circuit that the dog collar originally drove?

 

[meltedeyes]

So are you saying you that you determined your input to be .2v based on a DMM. If this is a pulsing signal I suspect a DMM will not give you what your input voltage really is. You need to use a scope or determine the signal from the design.

Correct. Unfortunately I don't have access to a scope. I have seen readings between .1xx and .4xx. I chose .2 as a reference to mitigate the inaccuracies of my DMM. I've been wanting a scope since I graduated 11 years ago, but could never justify the cost of the ones I've seen since until now I didn't have much of a use for one. But now that I'm starting to get some project ideas that require the knowledge from my degree...

 

[meltedeyes]

Maybe we can guess using another approach. What is the circuit that the dog collar originally drove?

The dog collar is one of the shock collars, so the circuit produce a mildly painful shock. I am using that shock as the input voltage. The product is an Innotek znd-1200 (Amazon.com: Innotek ZND-1200 Instant Pet Barrier with Receiver Collar and Zone: Kitchen & Dining) I have been unable to find much information on the collar's power usage. It's either not on the web or my google-fu has failed me.

I am using it as a kill switch on an electric wheelchair for when it gets too close to the transmitter which is near some stairs that can't be blockaded. I have a manual override to cut the power back in in the circuit I have built already and have been testing manually (ie plug wire into breadboard to simulate the collar tripping). I will try and get the schematics posted tonight or tomorrow. I'm sure someone here could recommend something better than I have designed.

 

[Mikebits]

Isn't the shocker signal some kind of high voltage?
One thing I been wondering. What happens once the Wheelchair is disabled, won't the person be stuck?

 

[meltedeyes]

The shocker may be high voltage, but the highest I've seen it go on my dmm is just shy of .5V

Yes, the wheelchair will be disabled, but that's the whole point of this. It's a safety measure that if everything goes well will never need to be used. But it is required. There is a manual override to allow the chair to move out of the range of the transmitter under it's own power. And it's either be unable to move for a couple minutes (high traffic area but a place he's not supposed to be) or not have a wheelchair at all.

 

[Speakerguy]

The shocker is way more than .5V... You gotta scope it.

 

[Mikebits]

I can't help but think your meter fuse may have blown after the first measurement on the dog collar. Have you tried to measure the voltage of a battery lately?

Cool idea, but I imagine the output current from this device is so low you could not even drive your mother in-law crazy (if you have one).

Perhaps a similar approach with something like a proximity alarm.