l293dne - a wierd monster!

[streamlinedwings]

i'm trying to operate 2 motors with a l293dne by taking inputs from m8870 dtmf decoder.. the following are my connections:

pin 1,9:   5v   
 4,5,12,13: gnd
pin 8: 6v (5.8 something)  // i'm using  motors which operate on 6 to 9v (not really sure)
2,7,10,15 : input pins (from the decoder)
3,6,11,14: connected to the motors

i've kept a 7805 to convert 6v to 5 for the enable pins and hav connected pin 8 directly to the battery (6v)..

the problem is: 1. as soon as i turn on the circuit(batt- on) without giving any inputs, one of my motor (the one connected to pin 3 and 6 ) gets started!!
// for this i hav checked my bread board twice thrice.. i observed that the pin 3 of l293dne was at some 5v..
also when i give a +5v at pin6 the motor shuts up! //
2. the motors run without enabling the l293dne (i.e. pins 1 and 9) how wierd??!
 I want to be sure whether i hav burned my l293dne ?? or not? what's going on!
//apologies for the length of my query//

[ankitbansal]

Seems you are not pulling enable pins to low.

"Without giving input" - doesn't mean its low.
Remember if enable pins are not connected to gnd or high. Then its in high impedence state/floating. And thus your motors would behave strangely.

Also 7805 usually has a voltage drop of ~1.2 volt. So suggest you to atleast use arnd 7v.
Hth.

Ankit

[Soeren]

Hi,

[...] Also 7805 usually has a voltage drop of ~1.2 volt. So suggest you to atleast use arnd 7v.

The regular 7805 has got a drop of at least 2.5V - some of them have a drop out of up to 3.5V.


Even an LDO regulator with a drop out of only 0.1V will have to give up regulation way before a 6V battery is exhausted.

[Soeren]

the following are my connections: [...]

How did you wire up the DTMF decoder and connected it to the L293?
Please post a schematic of how you made it if possible.

[streamlinedwings]

the following are my connections: [...]

How did you wire up the DTMF decoder and connected it to the L293?
Please post a schematic of how you made it if possible.

I have directly connected the output pins of m8870 (q1 to q4) to the inputs of l293dne (i.e. 2,7,10,15)

m8870(o.p 's)<----->l293dne(i/p's)
q1<-->pin 2 (1A)
q2<-->pin 7(2A)
q3<-->pin 10(3A)
q4<-->pin 15(4A)

have made pin1 (1,2EN) and pin 9(3,4EN) to +5v..
i connected 9v to vcc2 (pin8) and using a 7805 gave 5v to the pins 1,9,16(vcc1)..

in additional i hav used a 0.47uf (electrolytic capactior) in dtmfdecoder instead of 0.1 uf at pin1 (signal recieving end) ..and rest all are made as prescribed in the datasheet of m8870..(exactly)

to be more interactive with the m8870, i have connected 4 led's to each output pins(q1 to q4) with a 470ohm resistors each..and one led to ESt with a 470 ohm resistor
//I'm sorry i couldn't post a schematic as i don't know to use such a software as the EAGLE
I'm learning to use it as soon as possible//

[streamlinedwings]

Seems you are not pulling enable pins to low.

"Without giving input" - doesn't mean its low.
Remember if enable pins are not connected to gnd or high. Then its in high impedence state/floating. And thus your motors would behave strangely.

Also 7805 usually has a voltage drop of ~1.2 volt. So suggest you to atleast use arnd 7v.
Hth.

Ankit

yes..i even hav tried with a 9v eveready dry cell ...still the anomalous behaviour of the l293d..
i'm trying to connect each of the two motors to the two drivers of l293dne... when no inputs are given, (like you said)  there's this strange behaviour of one of the pins getting high.. but wait, when  there's some output shown by m8870 (when some of the pins are low and some are high) one of my motors which is getting 2 low inputs( =0v) is still turning on!
and more strangely that motor gets off when a high input is given..!(i.e. when it needs to be high it'snt and when it shouldn't be it is...) 
 

[streamlinedwings]

please..., help needed!

[ankitbansal]

Draw a schematic on paper. Click pic and post.