cd4541 timer schematic problem.

I have built a cd4541 based timer. timing can be changed by setting a dip switch. while the timer is running, oscillator is monitored using Q1 2n7000 and LED (thanks to RON h ).

After selected time the OUTPUT pin 8 is set high by timer. which in turn switches Q2 another 2n7000. and the output (jumper) should be set high.

while the timer is working file when built on a veroboard, it is not working on the pcb drawn by proteus (ISIS & ARES).

a) cd4541 oscillator is not working, and wrong voltages appear on PIN 1/2/3.
b) LED1 is continously high.

however when i remove both MOSFETS the timer works and output LED is lit after set time.

i suspect its due to some kind of schematic drawing error (which resulted in a bad PCB being routed by software). plz check MOSFETS connections and placements.

as you can see the Q2 source is not grounded and is connected to an OUTPUT Jumper from which i intend to get out for a small DC motor (100-200 ma current draw.) if this is a problem then how should i ground it and still get get output.

as this is my first schematic and pcb drawn by a software i would like to know if there is any error in it.

the PCB was autorouted.

muddasserniaz said:

as you can see the Q2 source is not grounded and is connected to an OUTPUT Jumper from which i intend to get out for a small DC motor (100-200 ma current draw.) if this is a problem then how should i ground it and still get get output.

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Hi, this is my opinion: the source of Q2 should be grounded; its load should be connected between its drain and Vdd (if it is a motor, don't forget to place a protection diode across its terminals).
BTW if you need 200 mA, that's the maximum (continuous) drain current allowed for the 2n7000. You may consider another MOSFET or an npn transistor.
You shouldn't have any problems with Q1, since it is connected properly.

hi,
Are you using the 4541 in 'single cycle mode' [as you have the MODE pin grounded]?

According to my datasheet, when used in this Mode, it requires a MR reset to restart, but MR appears to be also grounded.?

I don't see any supply decoupling on the pcb?

Eric

What is your battery voltage?
I would connect the gate of Q1 to pin1. Pin 3 is a high-impedance node, and Q1 gate capacitance may load it (although probably not a problem at your clock frequency).
I agree with Eng1 about the motor, and also with Eric's comments.

thanks for all the comments and suggestions.

Ron H said:

What is your battery voltage?

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i am using a 9v alkaline battery.

Ron H said:

I would connect the gate of Q1 to pin1. Pin 3 is a high-impedance node, and Q1 gate capacitance may load it (although probably not a problem at your clock frequency).
I agree with Eng1 about the motor, and also with Eric's comments.

Click to expand...

The frequency range is .5hz to 36hz max.

ericgibbs said:

I don't see any supply decoupling on the pcb?

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plz suggest decoupling capacitor value and placement.

ericgibbs said:

Are you using the 4541 in 'single cycle mode' [as you have the MODE pin grounded]?

According to my datasheet, when used in this Mode, it requires a MR reset to restart, but MR appears to be also grounded.?

Click to expand...

i wanted the prototype to be with minimal components and complexity, during tests i disconnect the battery to restart the timer. . i plan to include a switch in final pcb.

ericgibbs said:

hi,

I don't see any supply decoupling on the pcb?

Click to expand...

In the few years I've been experimenting with digital circuits, especially those involving timing (nearly all of them, eh), I've found many of the gliches and bobbles and quirks can be solved with bypass capacitors. It's like squirting lubricating oil on a squeaky bearing... everything smoothes out.

In digital work, I've found about 100uF does the trick. The value can go down as frequency goes up, as a rule, to the point where in audio and radio work caps in the picofarads are okay.

As the late T J Byers said in a recent Nuts and Volts column, "Many schematics that you find published in magazines and books leave the bypass capacitors out. It's assumed you KNOW to put them in."

Attachment shows a few examples.