Relay controlled by vero low voltage

[bloby]

Hello all

I'm working on the project for my uni study and part of it focuses on electronic solution. The problem is I'm a real beginner and just managed to solder my first kits. Anyway, I'm trying to trigger a relay (or something similar) with a very low voltage available (approximately 0.8-2V) and even smaller amps (in fact, the power generated comes either from a small motor originating from science-toy wind generator or from a lemon/potato). I have constructed and tested a kit called "monostable switch" and all works perfectly fine (an external button upon closing the circuit sends a signal to that kit, which then opens a relay and sends further connection signal). The problem is it is simply triggered by an actual closure of a circuit, not by a power generated by that potato

I want to have a possibility to demonstrate that in case potato or motor does not generate even a substantial amount of current, the button will not work, thus closing the circuit which then triggers external function.

I tried previously, with a different kit, just to power up that kit (as soon as it is powered, it will close the circuit via its built relay) with a use of let's say 11V batteries and connection of missing 1 volt (kit needs 12-15V to work) originating from that potato. It was however not generating enough amps as LED on that kit was pretty weak. I could connect more potatoes (although it is not good for my project) but I'm still not sure whether it will open a relay anyway. I have also read that I should not really connect batteries with different voltage on serial connection (although one of that batteries was an actual potato so probably any extra voltage will simply discharge in it, not causing any battery blow ups).

Is there possibly any device/relay, which would be powered by external battery but will act (open/close relay/circuit) upon sensing of a current from some other input device?

Any ideas much appreciated as I'm completely stuck! Many thanks in advance.

 

[ericgibbs]

hi and welcome,

The device you are looking for is called a 'comparator' , a common type is a LM393 IC.
Are you able to get a LM393 or LM339...??

 

[bloby]

Many thanks for that. I already got both of those at Maplin. I have no idea however how those should be connected :/

 

[ericgibbs]

Many thanks for that. I already got both of those at Maplin. I have no idea however how those should be connected :/

hi,
Thats good.
I will post a circuit diagram within the next 24 hrs, tell me what voltage your existing circuits are being powered by.???

 

[bloby]

My monostable switch kit requires 12V supply (555 Monostable Switch MAP 422 - N32FL). Thank you!

 

[ericgibbs]

My monostable switch kit requires 12V supply (555 Monostable Switch MAP 422 - N32FL). Thank you!

hi,
Its possible to trigger a 555 monostable directly from the output of a LM393, you dont really need a relay, would that be ok.??

 

[bloby]

If that is possible then it is perfectly fine with me, as I know that 555 has a relay already

 

[dougy83]

You don't even need to use a comparator - a simple transistor (or two) will suffice.

 

[ericgibbs]

If that is possible then it is perfectly fine with me, as I know that 555 has a relay already

Hi,
This works OK, can you follow it OK.?

Look it over, any problems ask..

Note:
There are two comparators in the LM393 IC. so you could make two circuits for different 555 if required.
The 10K SET pot allows you to set the trigger voltage between approx 0V and +1V

 

[ericgibbs]

You don't even need to use a comparator - a simple transistor (or two) will suffice.

hi Dougy,
From his description of his 'voltage sources' ie: potato/lemon batteries I would have thought a LM393 would be his best option, also IIUC he wants an adjustable threshold.?

Eric

 

[dougy83]

From his description of his 'voltage sources' ie: potato/lemon batteries I would have thought a LM393 would be his best option, also IIUC he wants an adjustable threshold.?

Hi Eric,

Sorry, I wasn't attacking your idea - I was merely stating another viable alternative option he might like to explore. An adjustable threshold is also possible when using a transistor by use of a potential divider.

Cheers
Doug.

 

[bloby]

Many thanks for Your help guys!!! I'll try working on it asap and kindly post questions (if there are any) again on this thread.

Again, thanks a lot. I really appreciate it

 

[MrDEB]

ONE BIG PROBLEM is the transistor is using too much power (.7v apx drop) There goes your potato battery voltage (1 potato)
Try turning on just one LED w/ one potato. WON"T HAPPEN
Lets see you want to use a potato to power a switch. No other power source?
I should go back and re read.

 

[ericgibbs]

Many thanks for Your help guys!!! I'll try working on it asap and kindly post questions (if there are any) again on this thread.

Again, thanks a lot. I really appreciate it

hi,
Lets know how Mr Potato power goes and lemon run on the circuit.
There was a thread sometime ago about using potatoes and other veggies as batteries.

 

[4pyros]

You should run the switch of a separate power sorce and trigger it with the low power.
Andy

 

[elexboi]

Is this a ladder switch(different voltage level switching)? Or just On & Off switcingh to your transistor?

 

[bloby]

You should run the switch of a separate power sorce and trigger it with the low power.
Andy

Does such switch exist?

 

[bloby]

On and off is enough for my purpose.

I'm waiting for an online video chat with my friend, who is more experienced than me as I will struggle building even that circuit that Ericgibbs provided and taking it to Maplins I was told the guy with electronic experience is out so could not even buy required equipment ;/

 

[ericgibbs]

Does such switch exist?

hi,
This is what I understand you are doing...
Using 12Vdc to power the 555 and LM393 and using a potato voltage to drive the LM393 input pins.???

 

[bloby]

Yes, you are correct. 555 already does what I want (it has a relay) but just with a simple button pressing (or external input connection, which works simply by joining both together, well like button does ) but obviously I want that LM 393 (or anything similiar) to trigger an input button in 555 but only when there is lemon current present.

In easier description, I just want to operate connection (I want to start a PC with it), which as you should know has a button and two wires to PC's motherboard. Those wires will send a signal when connected together (in that case a PC button). I want to trigger that start but only when lemon is connected. In fact, additionaly I am intending to incorporate additional small power generating device (a motor from windmill toy) and connect all together (plus small led indicators showing there actually is a voltage present from those sources, already have them), so when someone wants to start a PC, a lemon and/or motor needs to generate power. Otherwise, if they don't, the button will not work. It can have separate buttons, so one start button for lemon, one for motor or possibly only one but all joint together.

Hope that explanation gives better idea