Hi,
for those who don't want to buy a
20$ RSSI Buffer from DPCAV, here is a short how to build:
1. Why?
Because when you hook up the RSSI Output of the receiver direct to an OSD, some current is drawn from the receiver. In a few cases the voltage breaks down and can cause range problems.
So, here comes the buffer. It will copy the RSSI voltage and supplies enough current for the OSDs to measure the RSSI voltage.
No more problems.
The material costs are around 1-2 USD.
You will need an
Operational Amplifier and some servo cable and a Toroid Ferrite Core.
For the OP you will need a LM358.
We need to build an
Voltage follower
Its very easy to build this one.
I used a 2mm gold connector to connect the rssi buffer to the rssi output of my Futaba R1410DP.
Look at the photos, how i solder it together.
Quite easy.
5g with all connectors ready to use.
Works perfect.
Feel free to ask.
[
attachment=353]
[
attachment=354]
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attachment=355]
My OSD has a very big ADC input impedance.
Still I need this ?
A OP has an input impedance of ~100MOhm, i think thats much more than the OSD.
You can test it.
Measure the voltages of the receivers RSSI with TX on and TX off.
1x with nothing connected to RSSI
1x with OSD connected to RSSI
Than you can see the difference and if you need a servo buffer.
For example:
Futaba R1410DP
TX OFF: ~1,05V
TX OFF: ~0,10V (connected to TempA von Eagle Tree Datalogger v3)
TX ON: ~2,13V
TX ON: ~0,20V (connected to TempA von Eagle Tree Datalogger v3)
same test with a extra 10K resistor in series:
TX OFF: ~1,25V
TX OFF: ~0,11V (connected to TempA von Eagle Tree Datalogger v3)
TX ON: ~2,12V
TX ON: ~0,18V (connected to TempA von Eagle Tree Datalogger v3)
=> buffer is needed!
Futaba R149DP
TX OFF: ~1,10V
TX OFF: ~1,25V (connected to TempA von Eagle Tree Datalogger v3)
TX ON: ~2,05V
TX ON: ~1,98V (connected to TempA von Eagle Tree Datalogger v3)
=> buffer is not needed, but is safer for decoupling the RSSI voltage
Thomas Scherrer long range UHF RSSI -
Tx OFF : ~ 0.55 V
Tx ON : ~ 1.0 to 1.2 V
(01-22-2010 12:29 AM)BlueAngel Wrote: [ -> ]Hi,
for those who don't want to buy a 20$ RSSI Buffer from DPCAV, here is a short how to build:
1. Why?
Because when you hook up the RSSI Output of the receiver direct to an OSD, some current is drawn from the receiver. In a few cases the voltage breaks down and can cause range problems.
So, here comes the buffer. It will copy the RSSI voltage and supplies enough current for the OSDs to measure the RSSI voltage.
No more problems.
The material costs are around 1-2 USD.
You will need an Operational Amplifier and some servo cable and a Toroid Ferrite Core.
For the OP you will need a LM358.
We need to build an Voltage follower
Its very easy to build this one.
I used a 2mm gold connector to connect the rssi buffer to the rssi output of my Futaba R1410DP.
Look at the photos, how i solder it together.
Quite easy.
5g with all connectors ready to use.
Works perfect.
Feel free to ask.
Coming in late to this party I know, but I have a question. My RX seems to have an inverted RSSI output. 3V with TX off, and 1.8V with it on. So am I correct in thinking that all I have to do is use the inverting input, and then loop back to the positive side instead of the negative? This will still give me the buffering with an inverted output right? Or am I oversimplifying this?
Yes you are oversimplifying, that will not work.
The OSD has to handle that. Nothing to do with the buffer.
(09-16-2010 01:47 PM)BlueAngel Wrote: [ -> ]Yes you are oversimplifying, that will not work.
The OSD has to handle that. Nothing to do with the buffer.
So perhaps I need to put an OP-Amp Inverter between the buffer and the OSD? If so, I could just use the other side of the dual Op-Amp.
No. ;(
A Inverter does invert the signal.
that means:
3V => -3V
you don't want that.
You can built a Differential amplifier, but that is not necessary.
THE OSD does that job.
(09-16-2010 03:49 PM)BlueAngel Wrote: [ -> ]No. ;(
A Inverter does invert the signal.
that means:
3V => -3V
you don't want that.
You can built a .
OK. I get it. The re-scaling is done by the OSD, HOPEFULLY. Thanks!!
Hello Blue Angel,
I have a question for you concerning your own designed RSSI buffer.
In the pictures I see several wires and futaba like connectors.
Could you explain where this connectores go to?
I guess the white wire goes to the RSSI signal from the RX but the rest?
Thanks a lot in advance
(01-22-2010 12:29 AM)BlueAngel Wrote: [ -> ]Hi,
for those who don't want to buy a 20$ RSSI Buffer from DPCAV, here is a short how to build:
1. Why?
Because when you hook up the RSSI Output of the receiver direct to an OSD, some current is drawn from the receiver. In a few cases the voltage breaks down and can cause range problems.
So, here comes the buffer. It will copy the RSSI voltage and supplies enough current for the OSDs to measure the RSSI voltage.
No more problems.
The material costs are around 1-2 USD.
You will need an Operational Amplifier and some servo cable and a Toroid Ferrite Core.
For the OP you will need a LM358.
We need to build an Voltage follower
Its very easy to build this one.
I used a 2mm gold connector to connect the rssi buffer to the rssi output of my Futaba R1410DP.
Look at the photos, how i solder it together.
Quite easy.
5g with all connectors ready to use.
Works perfect.
Feel free to ask.