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ok so i guess I will chucking those LM7805 out of th house...
I have four 2300 nimh AA for my digital camera, guess I could use those for now, not need for voltage regulator right, just want to double check .
but with this setup , how would I have a regulated voltage to compare the batteries voltage, , How would I implement my blinking led for low voltage ?
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What are the implications is the unit's power runs out? (might help to figure that bit out if I knew how badly the unit had to stay powered up).Originally Posted by lerameur
How about this? Use a 2.5v reference chip from Microchip, MCP1525. Use that as Vref+ for an A/D input on the PIC. Take your battery pack, put a v-divider on it, say 2:1 ratio, 10K & 10K, or whatever, pluck the signal off the middle of that, read that to an A/D channel, and presto...instant voltage reading...with some math of course.
Ground on Vref-, 2.5v (from MCP1525) on Vref+.
Batt+ to one side of 40K resistor, Batt- to one side of 10K resistor. Other 2 ends of resistor connected together and fed to A/D input (say AN0 for example).
Do a read on AN0 A/D input. I forget what PIC you're using, but say it has a 10 bit A/D converter. That means that your 10 bit A/D converter would have a resolution (based on the 2.5v Vref+) of 2.44xxx mV. Since the voltage going into the converter is divided by 2, the real resolution of the total voltage across the battery is 4.8828125mV.
If you're project doesn't drain much current, you could probably run it down to about 3.6v (.9v/cell). So, while reading the A/D, your reading is going down. When it hits 737 (737 x .0048828125 = 3.598v), turn on the low battery light. Actually, you'll probably want the light on sooner to give yourself some time to get them charged up. And the MCP1525 comes in TO-92 & SOT-23 packages. Easy to use.
Last edited by skimask; - 31st December 2006 at 03:27.
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my father cuts meat and has a cold room in the garage, This unit is wireless receiver that will give him the temperature. It is not crucial if there is a downtime to charge the battery, (or a downtime of a few hours if the compressot breaks down) but at least a warning that they are running low.
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The transmitter is in the room and it's wireless/battery powered? And the receiver is elsewhere, plugged into the wall or something?
Ya know for that matter, you could (and probably are but I'm not sure), transmit the transmitter's battery voltage along with temperature data to the receiver.
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nope, the transmitter is in the garage, pluged into the wall, there is a 40 feet line runnin gfrom the sending module to the sensor, becasue the sensor is inside the fridge. This part is done, I installed the module up high inthe garage with the antenna sticking out, it is a straight line to the house. The receiving module is wireless, so he cantake it in his room or the kitchen etc..
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Ok, TX, powered, garage....
RX - portable, battery powered. Couple of notes I thought of. If the receiver doesn't get a good update for a minute or something, a light/alarm or something goes off as an indication to check on the transmitter (power went off or the transmitter got kicked over by the cat or something out there).
Have you already tried the TX module with this 40ft of wire? Does it work?
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yes the TX module is fully completed , I was doing my earlier test with it.
well also, i wanted to add a led for the battery alarm. A led for when the temperature goes over 50 F, and a piezo buzzer that gos off for 10 sec if the temperature goes over 50 F.
Last edited by lerameur; - 31st December 2006 at 03:47.
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