ASK RF module to L293D connection

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Hey,
I wanted to connect the outputs of the decoder to the inputs of a motordriver.Heres the problem, the output current rating of the HT12D was in the range of milli amps and the input current of the L293D was in the range of micro amps. IN the circuit i have attached, they have put 10k resistors, i really cant understand the math < wouldnt the voltage drop be so great that the voltage would always be a low at the inputs of the L293D?

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Lets say the HT12D can supply 5volts at the output. What current can flow? I=V/R, which is 5/10000 equals 0.0002A which is 200uA. I dare say the output of the HT12D can supply this and this current is in excess of the L298's input current requirement. So where's the problem?

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Sorry for my ignorance, if suppose i need a high at input 1, shouldn't 5V also come there? 5V-0.001*10000 (supposing 1 mA is the decoder output current), will give me -5. O_O

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10K might be too big to pull down the input to get 0V. 100ohms might work better? Why even have a series R? Just connect the decoder to the bridge? So all the brains is in the transmittr I guess. Whats the data rate into the decoder? 4800 bps? 12 bits in a word? So you get 300 updates per sec. Fast enough for speed and direction control. Seems Minimalist but Clever.

Imagecraft compiler user

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The decoder current rating is the amount of current it CAN supply. It does not force that much current to flow.

The current is defined by the load. In this case, the motor driver. Its input current is only a few micro-amperes. The decoder can easily supply that.

No resistors needed.

Yes, the input of the L293D is bipolar transistors, but they are PNPs working as emitter followers. So, its not at all like driving grounded emitter NPN inputs. You are safe without resistors.

Jim

 

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Quote:

Whats the data rate into the decoder?

maximum baud rate is 4800, to be on the safe side im using 2400.

Quote:
The decoder current rating is the amount of current it CAN supply. It does not force that much current to flow.

The current is defined by the load. In this case, the motor driver. Its input current is only a few micro-amperes. The decoder can easily supply that.

No resistors needed.

Yes, the input of the L293D is bipolar transistors, but they are PNPs working as emitter followers. So, its not at all like driving grounded emitter NPN inputs. You are safe without resistors.

Jim


Thanks a ton... that really cleared my doubts.. :)