Hi,

This Thread may be weird but happening in my RF System.

Designed an RF Board which was about to supply 5v to an RF Transceiver Module via LM1117 5V o/p and the input to the regulator was given from battery (7.4V, 3.35Ah).

When an external power supply (5V,1A) is directly connected to the the input pins of the board , The transceiver module is working properly and if i connect the battery to the input pins, the transceiver module is not working which means it is neither transmitting nor receiving any data.

The Important factor is that either connecting the external power supply or battery supply, the power goes through the voltage regulator and reached the RF module.

but Why it is working only with external power supply and not with the battery?

Someone help me out to sort this issue.

Thanks in Advance!

 

Have you checked polarity? Have you read voltage and current values on output of battery and output of power supply (LM1117?)? I mean really read, with a multimeter. From the little you've told us, it appears that your problem is supplying your needed power from your battery to your RF board, and that the "LM1117" is what you're using to do that. I have no idea if that "LM1117" is suitable for that job, but what you've presented is a troubleshooting problem more than questions about engineering of circuitry to power your RF board. I suspect you're overloading it, but without any better info, I could just as well suspect you haven't connected it.

 

An LM1117 (5v output version) will not supply 5 volts output when the input is 5 volts but it will supply 5 volts output from an input of 7.4 volts.
Your description is not very clear. Posting the schematic would make it easier to solve your problem. Have you measured the output voltage from the LM1117 in both situations ?

Les.

 

Have you checked polarity? Have you read voltage and current values on output of battery and output of power supply (LM1117?)? I mean really read, with a multimeter. From the little you've told us, it appears that your problem is supplying your needed power from your battery to your RF board, and that the "LM1117" is what you're using to do that. I have no idea if that "LM1117" is suitable for that job, but what you've presented is a troubleshooting problem more than questions about engineering of circuitry to power your RF board.

I had checked the voltage & current values at the battery end as well LM1117 end and it properly giving out 5V to the RF Module.

My important concern is why it is working with 5V,1A DC power Supply but not with 7.4v, 3.35Ah battery.

An LM1117 (5v output version) will not supply 5 volts output when the input is 5 volts but it will supply 5 volts output from an input of 7.4 volts.
Your description is not very clear. Posting the schematic would make it easier to solve your problem. Have you measured the output voltage from the LM1117 in both situations ?

Les.

 

Hi les,

Thanks for your response. Actually in both the vases the output of the LM1117 was tested with multimeter and it gives output of 5v directly feeding it to RF input supply.

My problem is why it is not working with battery and how it works with the direct power supply of 5v, 1A dc adapter feed.

Schematic will be posted in a day. Please let me know is there any problem with my regulator or do I need change the regulator with someother to get stabilized 5V to feed RF module.

Thanks,
SAI

 

All regulators have a dropout voltage. The LM1117 (5V) has a dropout voltage of 1.2 volts for an output current of 800mA. So you need at least 6.2 volts input to the regulator. My thinking was that your circuit was working when the output of the regulator was below 5 volts (Which it would be when fed with 5 volts input.) but not when it was 5 volts when it had an input of 7.4 volts.

Les.

 

You cannot be getting 5V out on both 7V battery and 5V power supply.
Check your circuit and measure the volts and report back. Then you may get some help.
But I think that Les may be on the right track.

 

All regulators have a dropout voltage. The LM1117 (5V) has a dropout voltage of 1.2 volts for an output current of 800mA. So you need at least 6.2 volts input to the regulator. My thinking was that your circuit was working when the output of the regulator was below 5 volts (Which it would be when fed with 5 volts input.) but not when it was 5 volts when it had an input of 7.4 volts.

Les.

Hi Les,

Here is the measurement data, measure across the Supply input, regulator input, Regulator output, Rf Input by connecting battery (7.4v, 3.35Ah) and 5v,2A Adapter supply.

While connecting Power Adapter Supply, module works fine

Input Supply: 5.06V
LM1117 Regulator Input: 5.06v
LM1117 Regulator Output: 4.06v
Rf Module Input: 4.04v

While connecting the battery (7.4V, 3.35Ah), RF module is not working.

Input Supply: 7.16V
LM1117 Regulator Input: 7.16v
LM1117 Regulator Output: 4.96v
Rf Module Input: 4.95v

I'm also posting the schematic in couple of hours for your reference.

why is that 900mV difference between both the power supplies, supplied at the RF input is not making the module to work?

Also the module is capable of working in both 3.3v & 5V

Thanks,

Saikumar

 

The regulator is not working on the power supply input as it needs over 6.2V in for 5V out. It looks like the problem is the RF module, not liking to run on 5V.

Why not use a 3.3V reg and then it will be the same for battery and power supply?
Maybe it will work ok on the 3.3V

 

The regulator is not working on the power supply input as it needs over 6.2V in for 5V out. It looks like the problem is the RF module, not liking to run on 5V.

Why not use a 3.3V reg and then it will be the same for battery and power supply?
Maybe it will work ok on the 3.3V

But in this case, battery power is sufficient to supply as the input to the regulator because its input is 7.15V. So it has to work and by the way in my circuit i had given a jumper to the rf module to switch for 3.3v operation.

Even i tried with working the RF Module for 3.3 V operation via battery and external power supply as the result remains same. it works with external power adapter and not with the battery.

 

Going by your measurements, it does not work on 5V. It is working on 4V.
The 5V power supply is not running it on 5V, but 4V as the regulator is not working because it needs 6.2V minimum.
Do you have a 3.3V regulator to replace the 5V one?

You say you tried 3.3V working, but did you try it on the 3.3V setting and running on the 5V? And I mean actual 5V, not the 5V regulator with only 4V out.

If so, you may have damaged it.

First thing you need to do is to get your power supply fixed. You cannot just use a 5V plug pack into a 5V regulator. That just will not work. Make up your mind what volts you want to run the RF module on and then get the supply going so that the output volts from your regulator is the same on the plug pack and the battery. That is why I think you should go to 3.3V and then you can use your 5V plug pack. Otherwise you will need to get a 9V plug pack for example.
And as it is working on 4V as you have measured it, just try to get your supply stable at 3.3V as that is a standard part you can get, and then your power supply variations will be gone.
Can you post the part number of the RF module and a circuit?

 

The 5V power supply is not running it on 5V, but 4V as the regulator is not working because it needs 6.2V minimum.
Do you have a 3.3V regulator to replace the 5V one?

if the regulator requires 6.2V minimum as input to work, then battery is sufficient to supply above that (7.16V) as measured. but it is not working. Yes i have LM1117, 3.3V regulator to replace the 5v one's.

You say you tried 3.3V working, but did you try it on the 3.3V setting and running on the 5V? And I mean actual 5V, not the 5V regulator with only 4V out.

No, I didn't directly connect the 5V input to the 3.3 node input end. Actual 3.3 V is supplied by putting a jumper so that the another LM1117 3.3V regulator on board will bypass its output to the RF Input.

First thing you need to do is to get your power supply fixed. You cannot just use a 5V plug pack into a 5V regulator. That just will not work. Make up your mind what volts you want to run the RF module on and then get the supply going so that the output volts from your regulator is the same on the plug pack and the battery. That is why I think you should go to 3.3V and then you can use your 5V plug pack. Otherwise you will need to get a 9V plug pack for example.

Even i tried giving the input through 9V,1A External Power Supply and running the RF Module at 5V. But it is not working. Also, the Battery is sufficient enough to supply as input to the 5V regulator and i'm weird that why is it working with equivalent supply but not with higher range input (either through power supply or through battery).

Can you post the part number of the RF module and a circuit?

Its actually E45 TTL 1W Lora Module from chinese

 

But that is the thing. It is only working on a 4V supply.
There is a lot missing. When you say it is not working, is it that you cannot talk to it?
If so, what are you using for the serial Comms?
It could be you are using 3.3V signals, and it is enough for 4V supply, but not swinging enough for 5V power.
Can you post a full diagram of your setup please.
You have been asked for more info, like a schematic, a number of times now.
We need to know your connections for whatever you are using to talk to it, as well as the power supply.
I don't know why you are stuck on feeding the 5V reg with 5V as one option. A number of times you have been told that is not the way to do it. Toss the 5V plug pack or install a 3.3V regulator. Get the power sorted out. You have probably 2 problems here and the power is one that is easy to fix. Choose 5V or 3.3V, not 4V and 5V!
Then tell us what the serial setup is.
If you really want help, pay attention to the advice.

 

What else is being powered by the battery/adaptor. It could be that there something other than the module that is misbehaving when supply with 5 V instead of 4 V.

Since we still haven't seen a schematic, it's hard to make guesses.

 

Not enough juice? It appear to only work on your 5V 2A supply.

http://www.cdebyte.com/en/product-view-news.aspx?id=189

 

Not enough juice? It appear to only work on your 5V 2A supply.

View attachment 143390

The problem is he is feeding through the 5V reg on both occasions and it cannot supply the 2 Amps.

He is saying it is working when he supply 4V, that is 5V plugpack into a 5V reg, but not when running on 5V when fed from the batteries into the reg.

Unfortunately, it is pretty hard to get real info and circuits from the TS so there is a lot of guesswork at the moment.
The power supply is a problem so that is why I'm trying to convince him to fix that first. And if he wants to keep the 5V plugpack, going to a 3.3V reg is the way to go.
I want to see the whole setup. There is no info as to how he is talking to it so there is a possibility is is a comms problem too.

 

The problem is he is feeding through the 5V reg on both occasions and it cannot supply the 2 Amps.

He is saying it is working when he supply 4V, that is 5V plugpack into a 5V reg, but not when running on 5V when fed from the batteries into the reg.

Unfortunately, it is pretty hard to get real info and circuits from the TS so there is a lot of guesswork at the moment.
The power supply is a problem so that is why I'm trying to convince him to fix that first. And if he wants to keep the 5V plugpack, going to a 3.3V reg is the way to go.
I want to see the whole setup. There is no info as to how he is talking to it so there is a possibility is is a comms problem too.

Hi dendad,

This is the schematic of the particular part causing power issues, Please let me know if anything is required more than this. Also, there is a picture of PCB, i had marked the component names.

Pl. don't consider the capacitors placed between the regulator in and out. It is for test purpose to suppress the oscillations and noise.

Thanks,
Saikumar

 

Well, I am convinced that you 7v battery and 9V 1A supply can’t supply the current the RF module it needs, as suggested in the datasheet, it needs 1.5A.

For reliability, replace the voltage regulator with a higher current one. Or measure the transient current draw and stick some bigger cap on the input of your RF module.

If doing continuous transmission, need to think about thermal management.

Also, I would use bigger trace for the Vcc. Or copper pour the Vcc as top layer?

I assume the PCB has a solid ground plane? As it will be part of the antenna, assuming you are not using a full wave antenna.

 

Maybe add some decoupling caps too, I don’t see any for your atmega328p

 

Yes Bug13, I agree. Those power traces are way too small. And the regs have next to no heatsinking.
Also, bypassing the CPU.

Pl. don't consider the capacitors placed between the regulator in and out. It is for test purpose to suppress the oscillations and noise.

They need to be removed.
Does anything work when running on 5V? I wonder if the problem is on the 5V supply, the transmitter RF is interfering with the rest of the circuit.
And maybe it tried to draw more current and resets the processor as the reg shuts down briefly.
An oscilloscope on the supply may help to work it out.
But the reg is nor good enough for the job. Cut the 5V feeding the radio and add another higher power reg for it. Then you have a separate clean supply for the cpu and radio. I tend to use the switch mode regs for a lot of my boards.
http://au.element14.com/tracopower/tsrn-1-2450/dc-dc-converter-1a-5v-5w/dp/2280247
These are pretty expensive so look to Ebay.
Try one of these..
https://www.ebay.com.au/itm/Voltage...885311?hash=item1ed219317f:g:RfMAAOSwke9Z6quW