I do not know if the relay can be switched using just the RF power, I have not tested it, but it seems a bit optimistic, even for these tiny relays.Does the rectified RF signal provide enough power to make the relay latch? Does it provide enough power if both coils are to be feed?
Hi,
maybe you can control it with two different frequencies.
Needs two bandpass filters with different frequencies. rectify the bandpass outputs independently and feed it to the two coils.
Applying one frequencie activates coil1, activating the other frequency activates coil2.
***
Battery powered antenna...is it useful? Whant´s the battery livetime?
Klaus
Hi,
does it need to be VHF or UHF? Why not 10kHz and 100kHz?
with one frequency you don´t have a feedback, and thus you can´t be sure if it is on or off.
With two independent frequencies you don´t have a feedback either, but maybe it is more reliable to switch to the state you want.
Btw:
If you want it to save battery power you may use a timer to switch it off, in case someone forgot...
And switch it ON with a long press, and switch it OFF with a short press.
Maybe it is possible to use a FET to switch On and OFF, then you don´t need to transmit that much power...
Or if it is UHF/VHF... is it possible to add filters, so you can supply it from remote? Transmitt all the needed power with DC. I have a DVBT antenna working this way.
Klaus
Hi,
a bjt draws no power when switched off.
Maybe protected high side FETs are an option.
I´m guessing there is an antenna cable. Where does it go to?
Klaus
The question is about dual coil latch relay, so it need to be activated only for some ten milliseconds. Or do you suggest a non-latching relays instead?How long time period are you intending the relays to stay active?
If you want a bistable (memory) circuit with zero quiescent current, you'll use a CMOS latch or FF.But a second look reveals that when tr1 is on, tr2 is off so one transistor will always draw some power from the battery, even if the circuit is supposed to switch off the power to the antenna. That is why I was thinking of the latch relay.
The question is about dual coil latch relay, so it need to be activated only for some ten milliseconds. Or do you suggest a non-latching relays instead?
If you want a bistable (memory) circuit with zero quiescent current, you'll use a CMOS latch or FF.
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It's a bit annoying that you are prescribing some application parameters (e.g. no DC can be feed through the antenna cable) without any reasoning. Not knowing the full story isn't particularly motivating...
Hi,
a bjt draws no power when switched off.
Klaus
This is not true. no active device is a perfect switch.
So you are a guruwow, for a guy that likes to hack ancient ham radio circuits and use regenerative receivers, you are getting all theoretical on us now?? For all intents and purposes, an "off" transistor has zero current draw.
I think one good way to measure such a small current is the decay voltage of a capacitor. For example take a 10uF capacitor. Charge it to 5V. Measure it after 1 minute, using your DVM. Still 5V or very close to that. Now try connecting your switched off transistor across the 10uF capacitor, and again measure voltage after 1 minute. If it is 0V, then you need a bigger capacitor. If it is still 5V, then you need a smaller capacitor. Once you have a capacitor where the voltage drops a reasonable amount after 1 minute, then you are able to calculate the charge loss in the capacitor and from that, approximately the current drawn. I think this is one way, there are others I'm sure. But certainly a DVM on 2mA scale won't show it, not on an OFF transistor, nor on a sleeping processor.
Hi,
or just read a datasheet.
In your schematics you use MMBT2222.
The datasheet says: I_EB0 (Emitter Cutoff Current) = max. 10nA.
(that equals to 300 MegOhms resistor, that might be in the range of flux residuals)
So now you could say "It is not zero". You are right.
I for myself knew that in fact it is not zero. But for your application it is compareable with zero, because the self discharge current of your battery is for sure more than 100 times then bjt current.
I have to learn to give the information more precisely. Maybe with the word "about zero" or "no considerable current".
Klaus
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