Of course, the processor will consume more power during the count/sense/write cycle, but it's still only on the order of a fraction of a mA, and it's only for a tiny fraction of a second. So at 8 seconds, you just count down from about 75 and when you hit zero, take a reading.
If you want one read every 10 minutes, you just decrement a counter which keeps track of the number of times the watchdog has timed out. Read the data, write it to your memory card and go back to sleep. Some Atmel processors have on-board temperature sensors, and you can use that, or if you want to use an external sensor, that's easy enough to do. When the watchdog timer times out, it jumps to an ISR that can do whatever you like. In this mode, the average power consumption is on the order of half a MICRO amp (about 1000 times less than your 555). You can set a watchdog timer to wake up every 8 seconds or so. The Atmel line offers processors with "pico power" operation. 555s waste too much power for your application - and you're going to have to record the data anyway, so why not use a micro controller and write to a memory card that you can just plug in and read later? That was when I found a simple variation on the basic circuit. I could use a 555 to generate a 1 second or slower pulse which I then feed into a counter to produce long and accurate delays but that seemed a bit of overkill. I want to have a delay that I can set from 10 minutes to a few hours. I began by testing the 555 in some conventional circuits and I was easily able to achieve repeatable delays of several minutes. I need a one shot timer that can energise the datalogger after a delay and be reset by the datalogger after it has performed the task. The 555 can be used in a number of different ways to produce square waves, pulses or simple one shot timing. I don't have any low power versions but I do have a standard one so I'm going to start testing that until I can get my hands on a low power version. The standard 555 chip takes 8mA but there is a low power CMOS version of the 555 which requires significantly less power to operate. If the timer power could be reduced to zero then the battery would last 30% longer. With an average current of 28mA the battery will only last for less than 3 days. If the logger takes 200mA when powered up then this is equivalent to 20mA continuous. This may be enough but this has to be put together with the power used by the datalogger when it's turned on for say 1 minute out of 10. This doesn't sound much but if you run the device off a 2000 mAH battery then it can only be expected to work for 10 days. I measured the current that one in-circuit 555 used at 8mA. The standard 555 IC has a low power consumption. It's been aroound almost as long as I can remember but it still manages to impress me with it's capabilities. The obvious place to look first when in need of a timing circuit is the 555 timer chip. To do this I need a low power, long time delay circuit to wake up the logger at regular intervals, take readings and transmit the data to a base station. I'm going to take advantage of the fact that I only need to record temperature every 10 minutes or more to minimise the average current consumption. Whatever I choose for the remote hardware it will need to be cheap to produce and low power enough to operate for several days at least on battery.
#Simple delay timer transistor circuit full#
I'm looking at various options to accomplish this from simple dumb sensors with a transmitter or a cheap microcontroller like the Arduino to full wifi enabled microcomputer systems like the Raspberry Pi. The information gained can then be used to optimise the heating system. I want to build an accurate picture of how the temperature varies from room to room and over time. I'm working on a project to allow me to wirelesssly measure and log the temperatures in a building. Long time delays with a 555 integrated circuit
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