![]() ![]() If the divider's resistors are too large that impedance will affect the accuracy of your readings because the total resistance of the lower resistor will be skewed slightly. You should not use resistors greater than around 10K in size on the input to the ADC because the ADC itself has a resistance (the impedance) which is placed in parallel to the lower resistor of the divider. When the P channel is OFF the only circuit connected to the ADC is the connection between the ADC input and ground through a 10K resistor, so everything is happy and safe. When DOUT goes HIGH it turns on the N channel MOSFET which then pulls the gate of the P channel MOSFET down to ground which then turns it on, thus connecting the divider to the battery. That means the gate of the P channel MOSFET is being pulled up to the battery voltage by the other 10K resistor, so the P channel MOSFET is off, which isolates the whole divider from the battery. The theory is, when the Arduino DOUT is either LOW or not connected ( pulled low by 10K resistor) the N channel MOSFET is turned off. This can be accomplished by using a P-channel MOSFET which you can then drive with an N-channel MOSFET: Instead of isolating the ground ( which leaves the battery then directly connected to the Arduino) you need to completely isolate the battery from the divider. The trick, though, is to do the exact opposite of what you are doing. if (tim = 10 ) system_sleep() // If confirmed battery low, enter sleep mode.I use a similar system on a product I recently worked on to monitor the battery voltage - and of course I didn't want it on all the time to drain the battery. int tim = 10 // Delay between low voltage checks float getVolts() // will do the delayed double-check next time. int MOSFETpin = 0 // MOSFET power switch gate signal int BATTpin = A3 // Analogue input from the 100K/22K divider. int LEDpin = 4 // LED flashes at power-down. const float vHigh = 13.75 // Set high voltage threshold (engine running). const float vLow = 13.50 // Set low voltage threshold (engine off). const float R1 = 99900.0 // R1 is nominally 100000.0 const float R2 = 21850.0 // R2 is nominally 22000.0 const float resDiv = (R2/(R1 + R2)) // Resistor divider factor applied to measured voltage. #define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV( bit))Ĭonst float Vref = 5.00 // Actual voltage and resistor values can be set here. * Car battery voltage monitor - .uk/arduino/car-voltage-monitor */ /* Uses ATtiny 85 with arduino-tiny core: */ The ATtiny85 should now be successfully programmed with the Car Battery Monitor sketch. They only apply if you're using an external parallel programmer so it's safe to Finally, load the Car Battery Monitor Sketch into the Arduino IDE and hit Upload in the usual way.This doesn't actually burn a bootloader in the ATtiny85 but it does set the internalįuses to match the board type we selected in step 5. Power up the Arduino Uno (with the USB cable), ensure the correct COM port is still selected and, from the Tools. ![]() From the Arduino Tools menu, select Programmer | Arduino as ISP.From the Arduino Tools | Board menu, select the ATtiny85 chip: ATtiny85 8 MHz (internal oscillator BOD disabled):.The capacitor 'absorbs' the auto-reset pulse from the USB/serial and prevents the Uno's ATmega328 seeing it. To do this,Ĭonnect a 10uF capacitor between RESET and GND on the Arduino Uno board (Capacitor negative to GND). When the Arduino Uno is acting as a programmer, it's necessary to disable its auto-reset circuit.(Uno pin designations) (actual IC pin numbers) Power down the Uno and connect it to the ATtiny85 as follows:.Selected in Tools | Boards and upload the ArduinoISP sketch to the Uno in the usual way: Open the Arduino IDE and open ArduinoISP from the Examples folder.Download the arduino-tiny library ( arduino-tiny) and, with the.There are dozens of websites detailing how to use the Arduino Uno as a programmer - particularly for the ATtiny85 - so I won't repeat them in detail here. The 'README' included in the downloaded zip package contains full instructions for installing it into the Arduino IDE. It's necessary to define the ATtiny85 core so the Arduino IDE knows about its pins.īe aware there are a couple of different libraries for the ATtiny85 that treat the ATting85's internal registers differently. The ATtiny85 is programmed using the Arduino environment with either an Arduino Uno or a dedicated programmer. Hammond Enclosure 50x35x17mm (Maplin code: N78BQ) Some Components Fused auxiliary socket plug It's just missing the 5.1v zener diode and the ATtiny85. This photo shows the PCB almost completed. These photos show, on the left, an enlarged layout of the PCB and, on the right, the actual-size artwork. ![]()
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