My question is generic in nature about electronics system design. I am trying to put together an RC car which is powered by an AVR Atmega168 chip. It communicates through an HC-12 module and has a quadruple h-bridge chip to move the tires. The schematics is as follows:

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The issue is that, without any load, the voltage regulator LM7805 will provide a stable 4.99v output on standalone basis. However, when put in the configuration below with micro-controller sending and receiving data, the voltage drops to 4.72v or so, depending upon how much current is drawn by the components. I am not an electronics engineer but I suppose any system which is powered by batteries must face similar issues and there must be general solution for such issues. In the schematics above, motor is being powered through 2 separate lipo batteries of 3.7v each. The voltage drop is therefore entirely by the 3 ICs.

  • \$\begingroup\$ Do you have any idea what current your load is drawing? If you do, can you please update the question, as this could be critical to knowing why the voltage has dropped by that amount \$\endgroup\$ – MCG May 31 '19 at 12:00
  • \$\begingroup\$ @MCG Note that motors have own battery \$\endgroup\$ – Russell McMahon May 31 '19 at 12:12
  • \$\begingroup\$ You need to establish (1) what are the parameters that affect the outcome (2) Are you lying :-) - ie do the motors REALLY not load the control 9V battery, | A 7805 is VERY old tech and has a typical min Vdropout = (Vin-Vout) 2v. ALSO there are MANY different versions- some are limited to 125 mA max output. You need to specify the model - a datasheet link like that one would help., Yours may be different. || Does the Vout drop occur when the motors are not present? When U4 is not connected to U1? || What is Vbat-(V when the Vout_7805 sags? \$\endgroup\$ – Russell McMahon May 31 '19 at 12:20
  • \$\begingroup\$ Well as embarrassing as it may sound, just realized that even the voltage across a simple wire on breadboard is coming out different. The wire that im using has very sharp end and sometimes tends to be not fully in contact. Perhaps its the simplest wiring issue \$\endgroup\$ – A. Munir May 31 '19 at 12:47

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