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Forum Index : Electronics : Wireless battery voltage display
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Downwind Guru  Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Would anyone have a use for a wireless battery voltage display. I have considered designing the circuit for a simple display that could be placed in the house to show what the current battery voltage is. This would be a indicator to show when your batteries are full charged or how low the battery voltage was getting, for off grid systems it would help to indicate when the need to reduce power consumption should be considered. The Data for the battery voltage would be sent wireless by a 433mhz transmitter from the battery location, to a receiver display module located in the house. I would do this as a kit form, as well as post all information on the circuit design for those who are able to copy it and make their own. 1:- Is this something that anyone would find a use for or be interested in. 2:- What form of display indication would be preferred, bearing in mind the display end choice will effect the cost of the project. Would a simple Red, Yellow, Green LED be enough, or maybe a LED bar graph block, Or would a LCD display be preferred. What thought do you have?? 3. Would you have it displaying 24/7 and supplied from a plug pack (Wallwart), or do battery operation with the need to press a switch to get a display reading. The cost of the 433mhz wireless modules is around $25.00 for the pair (RX&TX) and 2x microcontrollers (Picaxes) about $15.00 plus the other bits to the circuitry etc $xx.xx, if a LCD is added thats $10-30.00 depending on what is used. Cost adds up fast, so the choice of display is important to the cost as well as the desired result. If wireless Logging was being done, then the display could use the data sent out from the transmitter to the receiver for the computer, and would only require an extra receiver module for the display, the same transmitter could be used for both receivers. What is your thoughts of such a project and what preferences do you have with design and cost. Open to thoughts here. Pete. Sometimes it just works |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Pete Could this unit use an analog gauge as I would be interested in that. All the best Bob Foolin Around |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Hi Bob, I will need to think that through a bit as the picaxe only has A to D converters and not D to A converters. Im thinking it could be done using PWM, and maybe a millivolt meter, my first thought was a little VU meter like in the old stereos and portable radios of yesteryear had, some even had a battery scale on them, but no one sells them any more. I decided to make a start and use a LCD display and a 20x2 chip. What i am thinking is it could be used as a stand alone display or as the receiver for the computer in a logging application as well. That way if the computer screen is turned off to save power when logging you could still have some data displayed on the lcd like volts or amps or rpm. As a stand alone display and no logging it would only show volts, otherwise all the logging circuitry is needed to display more. Im still open to thoughts and preferences. Pete. Sometimes it just works |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Pete The other thing is to use a 3.5 digital meter as I see plenty of them but still analogue input. All the best Bob Foolin Around |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Why would you take a digital meter and make it analog and take a digital signal and make it analog to suit the meter?? I would think it better/easier to use the digital signal, and use a digital display with it. The only reason would be to stay with the 08m, 8 pin chip, but the 20 pin 20x2 is only $3.00 dearer and up to 16 times faster with at least 4 times more variables, and can drive a LCD direct without the need for a driver from its pinouts and still have enough I/O's for other functions. If you want a needle meter than one is stuck with analog. Pete. Sometimes it just works |
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oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Pete, You can buy digital multimeters for $1.00 US from china, (2.50 shipping)... just bought 2 ... one to leave in each vehicle for the "in case" things. This may make for a cheap digital read out, and lower project cost... just a thought. (I prefer analogue.. yes I'd try the PWM out to drive the analogue meter)... or to drive the elcheapo multimeter perhaps. ...........oztules Village idiot...or... just another hack out of his depth |
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Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1344 |
$1 US multimeters  wheres the link Oz I wouldn't mind a few....
Cheers Bryan |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Pete Go with the digital meter mate and the 20 pin as it may be used for logger apps as well Let me know how much and Ill send you some danerious. Hi OZ I would like a couple of those meters also as I dropped mine last week and now it no workee no moree. All the best Bob Foolin Around |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Hi Bob and Bryan ebay item They are actually US 99 cents each. Postage is 2.17 today, but no cheaper for the second one... exchange rate must be better than when I bought it perhaps ....so theyre cheaper still now. Makes a cheap digital readout. Not flash, but do the job.... but no auto switch off... but for a dollar I can live with that. Good back up meter for the car. May never use it, ....... but I might too. .........oztules edit....My postage was dearer for the first, and cheaper for the second ... now it is flat rate...... which is cheaper still... how do they do it??? Village idiot...or... just another hack out of his depth |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Thanks for the idea oz, and the link...I thought i was cheap with the $5.00 multimeters i got and put in everything so i always have one with me, with the hope i will never need it, and so far i havent needed it ...well except to fix eveyone elses crap. 
Its a scam as the battery will cost twice the price of the meter that is being sent 1/2 way around the world. Me thinks these are just the box the battery came in for someone else. I think i might stick with the budget end LCD even though they are $7.00 dearer than the multimeters, but at least i can write direct to the display, without the need to do PWM conversions. Im hoping to be able to select the data to display by toggling through the choices. If there is a wireless logger being used this should allow for AMPS are = XXXX, or Battery Volts are = XXXX or RPM is = XXX or even windspeed if monitored, even a tank level if one wanted. If no logger present then it would be just battery voltage displayed. This is all not really needed, but wireless is fun to play with and not that hard, so its intended as a learning project for anyone that might be interested in wetting their toes with a little project that has some practical use. At this point its just dots and lines on the screen for a circuit board design. Bob, Pop the credit card back in the pocket as there is a fair way to go yet. I could do a deal with you, and you write the software and i will do the hardware. ( then maybe i should stick with just a flashing led indicator)
Pete. Sometimes it just works |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Gee Pete, cd4026's are only 50 cents a piece (including postage), and then you can direct write to the multimeter lcd as well. I notice it has 28 input pads.. I assume 21 for the 3 digit segments, and the rest for dots and HV and - etc.... The lcd uses that foam interface to the board... so just throw the board out and use your board as a direct screw in replacement, and the screen would connect direct to that via the foam... (does that make it wireless?) It would give you something to do.... and you could pulse output to it with the 08M... and maybe use the meter case to put your board into...see I can make life ....interesting/ not worth living... (cross out that which is not applicable). Actually, the cd4026's and the meters are so dirt cheap, I may try and find the time to fiddle just out of curiosity..... the time seems to be the sticking point though at the moment. ...... Oz...(I can see Pete is bored and needs a project)..tules 
Village idiot...or... just another hack out of his depth |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
See Oz its working. It has inspired you to have a go. Bugger i cant win, i first get criticized for under engineering something than for over engineering something. I have another idea that is also wireless and will post a photo in a day or two. I have a workshop with lots of electronic bits and pieces that i tend to try to use, rather than buying more stuff to do a job with. The other problem is needing a micro with enough smarts to do the number crunching of raw data, to be feed out to a display. The 08m can do it if not to many functions are required. The present model has, a picaxe, a v-reg, a 433mhz receiver, a lcd and a handful of resistors and caps plus a couple of switches, i didnt think it could get much easier than that. My lcd only has 9 input pads including power and contrast. Pete. Sometimes it just works |
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GWatPE Senior Member  Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
I am not so sure about reverting back to basic building block counters to use as an LCD driver chip. It may be doable with a swag of other components, but Hitachi chips and LCD's are the way for a system with a micro. I use a 3 LED indicator on my own Wireless battery status indicator. The reciever is in a central location in the house, with the battery and transmitter being outside in another room, and it just indicates dumping power, power good, power OK, and power low, and really low power. A meter of any form is useful in the monitoring system, but an indicator does not need to be that complex. I have an LED display at the battery. Gordon. become more energy aware |
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SSW_squall Senior Member Joined: 20/03/2010 Location: AustraliaPosts: 111 |
I agree, 2x16 LCD screen is the way to go, they are dime a dozen commodity item. You don't have to look too far to find any peice of broken gear that can yield a screen for zero dollars. The Hitachi HD44780 controller is fairly straight forward to interface. Using it in 4bit mode and you can get away with it only taking up 6 I/O lines. You can also use the PIC to generate the contrast voltage with the PWM generator which can then be adjusted via the user interface. just my thoughts AB Einstein: Everything should be made as simple as possible, but not one bit simpler |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
Yes AB, For six bucks including postage.... it does beat the basic way.... but there is lots going on under the bonnet in those hd44780 things. Gordon, I don't think you need much more than 3 4026 chips and little else to drive any direct addressable 7 segment 3 digit screens. The three chips only need power, reset and a single enable and clk drive. Don't get any simpler than that There's elegant, and there's down and dirty..... I seem to fit the latter. 
............oztules Village idiot...or... just another hack out of his depth |
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| GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127 |
Hi Oztules, It is not quite as simple as you make it, as the primary function of a CD4026, is a counter. You would still need the voltage to frequency converter, and the 30Hz LCD refresh clock. LCD's do not live long with pure DC applied. Probably use a small micro to provide the necessary control signals. There is a lot going inside the Hitachi chips, for a useful purpose. This is getting a bit far from the point of this thread, relating really to a wireless signal for remote battery voltage indication. Gordon. become more energy aware |
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| Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
Oz got me thinking of a more simplistic wireless data transfer system. It has adjustable transmittion range and it will work with any language protocol, it is bidirectional. It is not limited to battery monitoring, and able to be used for endless functions. Very cost effective and should be well within anyones build capabilities. Extremely low power consumption. What do you think Oz?? 
Parts list available if anyone is interested Pete.
Sometimes it just works |
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| oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686 |
I don't see the mandatory rolling pin 
.........oztules Village idiot...or... just another hack out of his depth |
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| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1344 |
G'day Oz, Just bought 3 of them $11 Oz including shipping, now I do have a few LM7809's in the shed so no 9 volt batteries needed and these will make for bery cheap displays. Cheers Bryan |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Pete I have been thinking about what you you said about multi inputs, and I will throw the cat amongst the pigeons. What I would like to do is to monitor 3 phases output for the GTI 100 amps per phase max and input from solar 300 amps DC and input from windmills 300 amps DC, wind speed and feed to the house, ac 6000 watts max and 100 amps dc 24 volt charge to the batteries can be measured on the ac input line to the charger. I know its a bit of a contract but if it has multi input it may be possible to log all the above along with the battery voltage to a remote meter to save me leaving the computer in the shed in case the snake uses it for a belly heater. Also the led is blinking but I cant change it just stupid i think. All the best Bob Foolin Around |
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