Circuit diagram for Interfacing SIM300 GSM modem to A89S52

SIM300 is an GSM modem which can be controlled through AT Commands. In this tutorial i am going to explain how to send/receive sms, how to make/receive a call, how to send a tweet to twitter using the SIM300 modem.I am going to use the sim300 modem with TTL output so it can be directly connected to the microcontroller ports.Sim300 needs a power supply of 3.4v to 4.5v, but the microcontroller circuit has only 5v supply. I am just using a Diode 1N4007 in series with the Vcc of the modem. So a 0.6v...

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Simple Battery Level Monitor Circuit on Ultimate EC 2013

This simple circuit can monitor the charging process in 12 Volt Lead Acid battery or Tubular battery. The status of LED indicates whether the battery is accepting charge or not. It also indicates the full charge condition. The circuit can be incorporated in any battery charger like 6 volt, 9 volt, 12 volt etc. The only change needed is replacement of the Zener ZD with appropriate value. That is for 6 volt charger , use 6.1 volt Zener and for 9 volt charger it should be 9.1 volt Zener.  Battery...

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