I'm having a problem with MUX in my circuit. It's a strange problem. When I use MM74C151, circuit works as it should be. But when I use SN74LS151 replacing the MM74C151, circuit doesn't work as before. What could be the problem? I don't think there's any problem in SN74LS151 because I have three of those.
I'm having a problem with MUX in my circuit. It's a strange problem. When I use MM74C151, circuit works as it should be. But when I use SN74LS151 replacing the MM74C151, circuit doesn't work as before. What could be the problem? I don't think there's any problem in SN74LS151 because I have three of those.
May be the VCC of SN74LS151 doesn't support 5.9V. Coz I'm using a 7806. If I use 7805 another problem arises with my 6V relays which won't switch on at 4.9V. What should I do??
May be the VCC of SN74LS151 doesn't support 5.9V. Coz I'm using a 7806. If I use 7805 another problem arises with my 6V relays which won't switch on at 4.9V. What should I do??
Can't solve the problem. Here's my schematic. In my schematic where it says 5V, I have used +5.9V.And when I use MM74C151 it works fine but 74LS151 doesn't do what it should! hELP ME OUT!
Can't solve the problem. Here's my schematic. In my schematic where it says 5V, I have used +5.9V.And when I use MM74C151 it works fine but 74LS151 doesn't do what it should! hELP ME OUT!
Can't solve the problem. Here's my schematic. In my schematic where it says 5V, I have used +5.9V.And when I use MM74C151 it works fine but 74LS151 doesn't do what it should! hELP ME OUT!
hi,
I would say its the 741's thats the problem, powering them with a +5V rail, I suspect the outputs of the 741's do not goto thru the switching thresholds of the LS151's.
Can you measure the 741 outputs [high and low] and tell us what they are.?
A lousy old 741 opamp is not supposed to work when its supply is as low as only 5.9V.
If it does work, its output low voltage is about +1.2V.
The maximum allowed input low voltage for an old TTL IC like a 74LS151 is +0.8V so of course it won't work when fed from a 741 opamp.
The maximum allowed input low voltage for the Cmos 74C151 is +1.77V so of course it works.
Don't have any other op-amps. Which one do you recommend? This circuit is for a Line Follower which I have built. Do you think CMOS ICs would also give same problem after sometime?
hi,
Do you have access to the LM393 dual compartor.?
This would replace the 741 OPA compartors, use a 4K7 on the outputs of the LM393, a 1mA sink current should give a saturation voltage of < 0.5V.
The very simple circuit should have a high value resistor added for hysteresis as positive feedback so the circuit switches quickly at its threshold instead of amplifying noise or oscillating.
hi ruzfactor,
We seem to be going around in circles, the 741 is NOT suitable for this application.
Whats the point in 'fudging' the circuit to make it 'sort of work'.
A LM393 dual comparator will take up half the space on the pcb as 2 * 741 do, also it will consume less power from the battery pack.