What is the problem?

Question

I have made the following circuit, can anyone please tell me why the seven segments are flickering. I have used multiplexing, don't tell me it is because of that. I have tried it prototyping on an arduino uno and it worked perfectly.SO its not because of the multiplexing!! and its not the code. I think something is interfering or resetting the microcontroller because it does not store the values on the seven segments.The motors on the right are not connected. Any clue what is wrong?

balearicdynamics · Accepted Answer

Many thanks, Rishi! Well, first of all the power regulator without capacitors (and few other discrete components) is not the worth. At least it reduce the life of the battery, but it is very probable that one of the causes of the flickering depends on this, plus many other issues. About the problem os the regulator, it is very probable that you incur in the ripple issue. Whenever current is drawn from a regulator the voltage will start to drop but it is needed an amount of time before the regulator start increasing the voltage to compensate. This is the ripple effect. The amount of ripple will be larger if more current is drawn from the regulator so I suppose that when the system starts things seems going well but then the performances decreases as time go ahead; tale in account that the LM7805 as all this kind of regulators compensate the current with temperature dispersion so as time passes the system tend to be hot and the effect is more visibile.. To compensate the ripple effect just a capacitor provides a temporary bank of energy. This is used to keep the voltage stable. As source of inspiration please see the schematic in the image below. Hope you are not offending if I prefer that this part is set correctly before we take in consideration more in depth the circuit. I think that your excessive simplification may really create serious unwanted behavior to your system. Enrico

Former Member · Answer

Can the atmega actually source/sink the current needed by the display? maybe it's functioning within acceptable parameters to start with but it's probably becoming oversaturated and getting hot resulting in brownouts? 9v batteries don't supply a great amount of power either so definately a nicely sized smoothing cap on the power rails wouldn't go amiss either. -------------------- edit: Do you have a multimeter to check the voltages? If you are using a 7805, when they get hot they also start pulsing on and off so just check to make sure it's capable of supplying the current you need and also a temperature check while it's in operation would remove that doubt. Lucie

mcb1 · Answer

rishi2628 This has echos of this post, where the same circuit worked when the servo was disconnected. http://www.element14.com/community/thread/42034/l/servo-problem Despite several people helping, you stopped replying on the 27th, yet this new post suggests the problem wasn't resolved. I see several problems if this is built as shown. 1. The ground from R1, R2 is missing....I'm assuming its is a simple error of the schematic, but maybe not. 2. I see no capacitors across the supply. and especially the digitally noisy 7 seg LED's. 3. Pin 13 (PD7) is floating, so either the schematic has another error, or that is the way it's been wired. 
 This battery is driving the microcontroller and 2 pwm servos that will be connected at pins 16 and 17

In nearly every 'HELP' call when servos are included the OP has failed to add a 1000uF capacitor or power the servos separately, and this has been the cause of various issues. Does it perform Okay with the servos disconnected.?? (Your previous post suggests the answer is YES) I might help if you include your code, however I do think its is a supply issue. In future it is always beneficial to those trying to help to include ALL the schematic. This includes the Regulator, Filtering capacitors, and connections to the device ...7 seg LED's PWM Servos. Enrico is correct the ground connection is not shown on this schematic. While the internet is great at passing information, it doesn't work well with crystal balls, and visibility beyond what is supplied ... Mark

rishi2628 · Answer

Try to open the image in new tab for a magnified image. Let me make it easy for those who do not understand the circuit...................... the top row of push button is for the each seven segment respectively. The bottom row is reset and set. Now i am providing 5 volts using 7805 ic and a single 9v battery. This battery is driving the microcontroller and 2 pwm servos that will be connected at pins 16 and 17. As soon as i give power the 7 segments are on and they work ok but after a while they start to flicker and the values stored on the 7 segment become 0(the default values). My guess is that the microcontroller is some how resetting or the 7805 is not providing a continuous 5 v supply. Any clue what is happening?

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