constant 4.5 V supply using batteries?

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PcAx anothermarc

Member
how may i get a constant power supply of 4.5 Volt
using batteries?


--------------------------------------------------------------
WHAT I FOUND SO FAR


googling and visiting several discussion groups
i found related advice ...
- e.g. using 1 more than the required batteries
in combination with e.g. a voltage regulator, diode, resistor, DAC -


if i use 4 instead of 3 aa batteries
and the voltage drops after a while -
would a voltage regulator, resistor, DAC guarantee
still provide 4.5V from the remaining voltage?


may i ask you what you would recommend?


--------------------------------------------------------------
WHAT I NEED IT FOR


i am using rf sender/receiver modules
with my picaxe 08m microcontrollers
&
found, that they (and the connected antennas)
work best at a constant voltage of 4.5 V
 
W

westaust55

Moderator
Firstly, you have posted in the Finished User Project section.
For questions you should post in the Active PICAXE forum section here: http://www.picaxeforum.co.uk/forumdisplay.php?2

If you use just one extra battery cell then the higher voltage will nominally be around 1.5 volts greater than the desired output.
With fresh fully charged batteries this will be more but with seriously depleted/flattened battereies the voltage difference between input to output across the regulator may only be a fraction of a volt.

Do not consider a diode, either simple silicon or zener diode, as the voltage if not as constant as some perceive but will vary with current through the diode.

Voltage regulators such as the 78xx series have a drop out voltage of around 2 Volts so the input voltage must be more than 2 Volts greater than the output.


Low Drop out regulators such as the 78Lxx LM2950 series have a drop out voltage of around 0.04 to 0.38 Volts.
There are regulators for fixed voltages such as 3.0 V, 3.3 V 5.0 V etc but I am personally not aware of a fixed regulator for 4.5 V
You will need to therefore use an adjustable low drop out variable voltage regulator.

Which Rx and Tx units are you considering?
Some simple units do indicate Tx voltages such as 4.0 V or 4.5 V but in reality work far better at 5.0V.
 
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westaust55

Moderator
True Nick12ab. Momentary confusion - fixed above to avoid confusion
(Heck, I even use the LM2950 series myself in fixed values)
 
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PcAx anothermarc

Member
... thanks a lot for your immediate & helpful advice, westaus -
sounds like this is the solution;
will try to find an
adjustable low drop out variable voltage regulator!

and yes - taking a 2nd look at the datasheets
the receiver module is min 4.5 V, typical 5V ...

would it do harm to my circuit if i added
a 5V battery instead of the 3aa (4.5V) batteries?
(am a newbee to electronics hence i hope you'll forgive this question)

--------------------------------------------------------------------------------
your advice

regulators' advice

adjustable low drop out variable voltage regulator:

Low Drop out regulators ( LM2950 series ...)
with an input voltage more than 0.25 Volts greater than the output
(they work on less voltage than the standard regulators such as the 78xx series)


No diode
... as the voltage is not constant



--------------------------------------------------------------------------------
My Rx and Tx units:

433*MHz AM-Sender
http://de.rs-online.com/web/p/hf-module/6172072/

... datasheet specification for voltage:
Wide Operating Voltage (1.5-5v)


433MHz AM, Super Regenerative Receiver
http://de.rs-online.com/web/p/hf-module/7154066/

... datasheet specification for voltage:
Supply Voltage Min: 4.5V Typical: 5 V Max: 5 V




--------------------------------------------------------------------------------
... wrong forum:

please accept my apologies for this;
i thought i posted it within the "miscelleanous" section ...
can i shift this onto active forum?


best regards!
marc
 
M

manuka

Senior Member
Westie has already corrected this, but the 78Lxx series are just low current versions (~100mA max output) of the normal 78XX 3 terminal regulators. I seriously doubt that the RX/TX units mentioned need exactly 4.5V anyway. In my experiences with such modules most TX are quite happy with anything from 3 V -6V ( & in some cases even 12 V. It's the RX that are picky, & most insist on 5 V +/- ¼V. But EXACTLY what units are you using ( & just what are you doing) please?

The electrochemistry of cells means only certain voltages (& their multiples) are possible - hence carbon-zinc 1.5V, NiCd/NiMH 1.2V, lead-acid 2V etc.

Extra: You've just replied ! Those RX/TX modules look similar to zillions of other basic ones around, so just initially run them on 3 very fresh AA alkaline batteries. These usually have terminal voltages ~1.6 + Volts each, so hence 3 x 1.6V += a good 4.8V-5V supply. I long used this approach to good effect when quickly testing all manner of portable devices needing 5V +/- ½V. A lab power supply or LDO ( low drop out) regulator circuit (or even these days USB outlet) is normally better longer term or if indoors near the mains of course!
 
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westaust55

Moderator
I have moved your post to the Active forum section. There is only a link remaining in the Finished Projects area now.

There is no battery available (to my knowledge as a 5V battery). Nominal 6 Volts comprising 4 x 1.5 V cells internally yes.
Four rechargeable NiMh cells are around 1.25 x 4 = 5 Volts but fully charged are approx 1.3 to 1.4 Volts each

So as a better solution with generlaly constant voltage you could use a low drop out LM2950-50 to achieve 5.0 V from four 1.5 V cells.

EDIT:
I see the Tx module is 1.5 V min, 3 V typical and 5 V max.

The Rx module is 4.5V min, 5 V typical and 5.5 V max.
 
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PcAx anothermarc

Member
thanks for moving the thread, westaus
&
the 4 1.5V - with - low drop out LM2950-50 - battery hint.

and thank you, manuka, too:

you are right ... i found that using fresh batteries
increases the power significantly -
am able to send signals through 5 (!) 25 cm stone walls
with a new/recharged set whereas
having ca. 4 Volt on each (receiver/sender)
hardly go through more than 2 walls.

this was extremely helpful -
i already started using different antennas
to improve my modules' power with no impact at all

thanks, again, to all of you!
 
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manuka

Senior Member
Great- you'll generally get better range with slower data rates too. Try even 300 bps? What are you monitoring ? All sorts of simple 433 MHz antenna can be organised, but perhaps a Yagi or Slim JIM may suit. Do you know about these? Note -some countries do not allow a TX antenna however.
 
P

PcAx anothermarc

Member
i would love to try 300+ mhz but being based in germany
i've heard that this frequence is not for official over here.

thank you for the hint:
i have heard about the magic of the yagi & slim jim but i am afraid
that they might turn out to be just too large (eventhough sending much stronger signals for sure)
- same for the "moxon" antenna which is mentioned quite often when it comes to
powerful antennas ...

i try to keep the antenna as small as possible -
in fact i do use just 2 ca. 19 cm copper wires as a kind of whip antenna at the moment
... the exact size was calculated based on quarterwave length ...
(will try some ca. 10 cm dorji antennas soon ).


....
i do have 433 mhz dorji modules as an alternative set of rf modules-
though i couldn't try them yet i've heard that they are far better than my 433 mhz ASK modules -
and might enhance the signals' power


... i am just measuring light intensity (at the moment)
using a simple LED based device with a receiver on the first floor whilst
the second device (receiver connected to laptop) is based on the ground floor -
already thought about a "helica"l antenna to keep things small
but this seems to work only/best when one touches it - like with a mobile phone's
antenna

thanks a lot, again!
 
P

PcAx anothermarc

Member
i knew i was too enthusiastic
since i forgot about my extremely limited skills/knowledge;

i googled / had a look at the links at farnell/rscomponents' dataheets ...
(please see excerpts within the screenshot attached )
... and could not figure out
what capacitors/resistors i need to add
to whether the MIC39100 or LM2931
in order to convert the batteries' 6volt
to 5volt necessary for the circuit -

bothB.jpg

may you give me any additional hints -
i appreciate!
 

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D

Dippy

Moderator
MIC39100-5.0
Data Sheet has 2 sections you should read.
"Input Capacitor" and "Output Capacitor".
Both sections are on Page 9 of the Data Sheet I have.
Both sections recommend values and types. You should read the notes.


LM2931.
Values are shown on page 4 of the Data Sheet I have."Typical Applications".


For low current apps also look at LM2936.
 
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manuka

Senior Member
i do have 433 mhz dorji modules as an alternative set of rf modules-
though i couldn't try them yet i've heard that they are far better than my 433 mhz ASK modules -
and might enhance the signals' power
Click to expand...
If these are the same ones mentioned here, then the link performance indeed should be greatly enhanced. They've also very flexible supply needs (~3.4- 5.5V) so your voltage regulation will hence not even be needed!

N.B. Transmit antenna shouldn't really be called "powerful" as they work by more suitably beaming omnidirectional signals. Although some resonant effects can arise, essentially the same transmitted power is still being handled.
 
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PcAx anothermarc

Member
@dippy -
thanks ...

i had a 2nd look and found the information as in the following
... but i am not sure, if these specifications apply to
a conversion from 6V to 5V (?)

-----------------------------------------------
MIC39100

" ....
Input Capacitor
...
when device > 4 inches away from bulk ac supply capacitance
or
when supply = battery:
capacitor >= 1μF or greater

Higher capacitance values
help to improve transient response
and ripple rejection and reduce output noise. "


Output

"...
output capacitor
>= 10μF .... ESR less than 2Ω ...
low-ESR solid tantalum or aluminium electrolytics capacitor
..."

-----------------------------------------------
LM2931

send2931.jpg
 
P

PcAx anothermarc

Member
@ manuka -
yes! i have the "yellowish orange ones" ... 434 MHz modules -
am happy to hear that they might not even need the 4,5V or even 5V.

(on annother note i'd like to mention that the shipping to europe was extremely fast ...
i ordered them on a friday & received them on monday ... just 4 days later -
the enquiries i sent were answered -even on a sunday- in a very helpful as well as professional manner
from kind & patient Mr. Yao within hours eventhough dorji is based in china!)
 
P

PcAx anothermarc

Member
summary - in-between results

Thanks for all of your comments & hints-
since there were a lot of great information
&
i am not too sure what too choose now
i tried to summarize what i got so far
- hope that i understood/listed it
in a way that makes sense - :

------------------------------------------------
my specifications

http://imageshack.us/photo/my-images/441/1specsm.jpg/

------------------------------------------------
in addition to your hints:
charts to choose a suitable
regulator

http://imageshack.us/photo/my-images/850/2choosing.jpg/

------------------------------------------------
3 adjustable regulators
http://imageshack.us/photo/my-images/819/3a39100.jpg/
http://imageshack.us/photo/my-images/35/3b2931.jpg/
http://imageshack.us/photo/my-images/822/3c2981.jpg/



------------------------------------------------
1 fixed regulator
http://imageshack.us/photo/my-images/23/47800.jpg/



which one should i choose for

a constant power supply of 5 Volt
using
4 aa batteries/cells (ca. 6Volt)
running
433MHz rf sender/receiver modules ?
 

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manuka

Senior Member
PcAxetc: WHAT EXACTLY ARE YOUR 433 MHz INTENTIONS ? If you are just "having a play around" then a simple 3 xAA battery setup should be perfectly suitable.If you use 4 xAA then NiCd/NiMH could be used instead, or even somewhat older ( & thus lower terminal voltage) regular C-Zn/Alk batteries. As already stated, most modules are not that demanding on the supply voltage anyway. The whole electronics industry has moved to more flexible supply needs as well - PICAXEs being typical with their ~3V - 5.5V needs. For proof of concept work,when portable testing is involved, battery power is usually ideal.

But if you are seriously needing a long term 5V power supply (LDO reg.based) then perhaps specify how the energy is to be delivered- from the mains perhaps via a plug pak? You can often pick up 5V ex cell phone chargers for peanuts of course now- many thrift shops have boxes of them selling for just a few euro.

Glad you also found Mark at Dorji helpful,prompt & friendly- such considerations go a long way in business!
 
P

PcAx anothermarc

Member
@manuka

thanks for your reply & the hints!

i thought i can prolong a constant 4.5 or 5 volt on my circuit
using an additional battery for each: sender/receiver ;
a kind of "backup" that provides the missing power
once my 3 aa(a) batteries (or cells )
do not provide the necessary power anymore
to guarantee that the rf modules' signals can pass
enough walls in order to communicate with each other;

since my sender module should be mobile (i want it to be able
to send signals from outside the house) i would like to keep it off any plugs
and recharge the batteries as few times as possible.

saying that - some of my modules will be used nearby a plug:
i can use a mobile recharger instead of batteries for those -
thanks a lot for the hint !



@marcwolf

thanks a lot for hinting me towards the booster -
it's a great device since it allows for setting/trimming the voltage manually
within a suitable and even larger voltage range than i would need it!

i did not mention that i want to use a set of batteries without
replacing/recharging them for an as-long-as-possible period;

since the booster requires a lower input than output voltage
i fear that i would uncharge my batteries with the booster sooner
than with an +1 battery / voltage regulator version.

but - will definitely have to try this option since it is
providing a constant voltage - thanks, again for this hint!
 
W

westaust55

Moderator
Efficiency is certainly a topic to consider for long term operation.

With a low drop out voltage regulator, the losses equate to the quiescent current and load current relative to the voltages involved. Lets say you have 4 x 1.5 Volt cells and a load current of around 10mA.
The quiescent losses are ~5 mA X 6 V = 0.03 Watts. The load current based losses are 10 mA x (6 – 5=) 1 Volt = 0.01 Watts thus the total losses would be 0.04 Watts. Efficiency relative to power demand (10 mA @ 5 Volt = 0.05 W) = 0.05 / (0.04 + 0.05) = = > 55%

By comparison the efficiency of the pololu module that marcwolf has given a link to with say 3 V input and 5 V output will be around approx 65% (as derived within the accuracy of the available curves).
 
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manuka

Senior Member
PcAx etc: OK, so only the transmitter is away from the mains, but PLEASE DETAIL JUST WHAT YOU ARE ACTUALLY MEASURING and HOW OFTEN ! When ever portable power needs arise such overview insights are crucial- often a major issue with off grid dwellings of course! It can be futile sweating the details when key aspects are neglected - perhaps akin to designing a fire breathing car for yourself & forgotting such "trivial" things as it's thirst for costly fuel...

A field 433 MHz transmitter with just occasional transmissions may have such a low duty cycle that it's battery drain may be near shelf life. Andrew Hornblow & I have been doing hibernation tests on 3 x AA powered (& 08M2 controlled) Dorji DRF7020 modules, & with transmissions every few minutes current drains averaged well <1mA. Such a scheme means 3 (or 4) x alkaline AAs (each of capacity ~2500 mAh) should last months. For proof of concept work this may be totally satisfactory.

Extra: Andrew, who is legendary for his PICAXE minimalism,splutters that "a mA is far too high", & now is eyeing up microAmp averages.
 
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PcAx anothermarc

Member
@westaus -

i am an extreme low-level hobbyist when it comes to electronics -
please forgive me for not being able to follow your calculations in detail;

i understand that i was wrong saying that the polulu booster is less effective
than a voltage regulator solution
since the booster's efficiency is > approx 65%
whereas a low drop out voltage regulator's solution results in > 55% efficiency.

if this is true then i should choose the polulu booster instead of a voltage regulator!


@manuka -


please accept my apologies for not providing enough information -
and thanks a lot for your patience with my enquiries!

--------------------------------------------------
THE CODE / SENDER & RECEIVER's MESSAGE FREQUENCE

derived from instructable's Richaarddd's project
my circuits send signals every 5 seconds;
http://www.instructables.com/id/Wireless-temperature-sensor/step3/Writing-the-Receiver-Code/

--------------------------------------------------
THE CIRCUIT

i modified the circuit to use two 08m2 chips instead of
a 08m2 and a 18x chip & i did not use a seven segment display;
-
the led's do indicate if sending/receiving works,
the sensor's value is received on my laptop's
macaxepad
-
-------- the circuit
http://imageshack.us/photo/my-images/8/receiverq.jpg/
http://imageshack.us/photo/my-images/706/senderx.jpg/
http://imageshack.us/photo/my-images/684/mycircuit.jpg/



--------------------------------------------------
CONSTANT POWER SOURCE /
(i think that i) CAN NOT USE DORJI's (in this case)

the potientometer is a placeholder for the sensor
(which is an led measuring the intensity of light)

the only pin left unused on the sender's circuit
is port #4, the "C.3" pin;
the sensor is connected to port #4, the "C.4" pin.
i think that i can not use a dorji modules (which might need less power)
since they would need 2 pins to connect
to the 08M2:
-
dorji pin 5 to 08m2 #3, "C.4" (this one is taken by the sensor)
dorji pin 4 to 08m2 #5, "C.2"
-

this is why i would like to stick to the "ASK" rf modules
&
i noticed, that these "ASK" rf modules provide enough signal's strength
to pass through several walls once i do have enough voltage;
(i started this enquiry to find a solution on how to
prolong the batteries' life ... )
 

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manuka

Senior Member
Aha- now we're getting somewhere! So it looks as if you want to measure a remote temperature & wirelessly send this thru' a few walls for indoor display ? Could you please confirm this before going any further ...

Ambient temp. measurement an easy task for a PICAXE friendly DS18B20 sensor, 08M(2) & ASK transmitter, & if the outdoor temp. doesn't vary too rapidly then you don't even need to send it very often either (meaning battery saving SLEEP can be used). Perhaps the greatest issue is just how you'll "read" this temp. indoors. Perhaps consider a sequential 7 segment LED approach ?
 
P

PcAx anothermarc

Member
thanks for posting the links ...
i like the idea of adding just one 7 segment display (looks nice & is functional)
though all i need is to get the data onto my computer.

my "sensor" (light measuring LED or trimpot) is far less demanding/difficult
to code/read than a temperature sensor *-
it's an implementation of Richardd's script
but without his temperature-to-segment-display code

* my sender's message holds information about ...
VOLTAGE BATTERY (SENDER) ---- via string /DATA_RCVD_SIGN = 42 ...(42 being a sample value)
TRIMPOT VALUE or LiGHT MEASUREMENT (SENDER) ---- via string / DATA_RCVD = 199 ...(199 being a sample value)
message end index (SENDER + RECEIVER) ---- via string / CHECK_DATA = 120 ...(120 being a sample value)
 
M

manuka

Senior Member
"Light measure" = Daylight ? Artificial? How rapidly does it change ? Trimpot? Richardd's script ? Why the need anyway? Horticulture ?

LDRs (Light Dependant Resistors) are the classic way to measure illumination,although some clever approaches have emerged with LEDs. LDRs typically present ~1k resistance in sunlight & ~1 Meg Ohm in darkness. Such R values are very easy to read with via PICAXE READADC at the mid point of a voltage divider.

It's past my bedtime ... Stan.
 
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Marcwolf

Senior Member
Hi all
The Pololu booster will handle voltages greater than it's output however if IN voltage is more than double the OUT voltage then the OUT voltage will not be stable.

However I do believe that if the OUT voltage is about 4.5V and you put in 6V then it should track ok all the way down.


Re the circuits - having a quick look at them - to save power on the trasnmit side you can always get the Picaxe to turn on the transmitter just before it is going to send data. That way it can really go into a deep sleep mode for 4.8 seconds then wake up, take its reading, turn transmitter on, send data, and go back to sleep again.

Hope this helps
Dave
 
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PcAx anothermarc

Member
@ manuka
it's actually both: measuring daylight & artificial light
changing at short term intervals (light switches within the house) and sunlight at day time

i used a trimpot for testing the values sent/received by the receiver/transmitter
- an easy-to-use placeholder for a sensor's input.

once i got everything done i might add pressure/sound/ultrasonic ... other sensors;
the main idea behind all this is to find out about how i can measure & access
sensor data & transfer them to my computer - and how difficult it is to do so
being an absolute beginner like me - that's why i started with a simple light sensor.

i found richardd's circuit when searching/googling for "picaxe rf sender receiver circuit".
from my point of view it is one of the most clear circuits/scripts i found
using cheap but effective components whilst embedding a lot of features
(2 different led's monitoring of the data sent,
an additional 7 segment display, ...)
 
P

PcAx anothermarc

Member
@Marcwolf

Thanks a lot for the information!
i was not sure about the required/allowed input/output voltage ratio
since there is a note refering to it on the booster's webpage ...
but
since you mention that there's no danger using it for my purposes
i should definitely give it a try
(besides - there are a lot of other polulu voltage regulators -
will have a look at them too ...)
&
i did not really work on coding the receiver to switch off when it is not used -
this will help to prolong the batteries' life for sure.

thanks, again!
 
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