## Time domain simulation - Time step

 Dear Sir, when I simulate NE555 regulator I noticed that the frequency at the output depends on Time step that I choose.For example for the same resistors and capacitor values when I change Step time the frenquency changes.For Time step 1ms frequency is 500Hz and for Time step 10ms the frequency is 50Hz.How would you explain this?The frequency shouldn't depend on Time step. by programerbg December 30, 2014 Can you calculate the expected frequency out of the 555 based on the connected components (resistors and caps)? The output frequency may be very high and the simulation is experancing aliasing. by Garrett December 30, 2014 When I calculate it I get the expected frequency.Thank You by programerbg December 30, 2014 Could You help me I have another issu.You can view my project on the link:https://www.circuitlab.com/circuit/qvhcmt/differential-amplifier/ . Amplification is 25 and the voltage difference is 200mV but insted of getting 5 V at the output I get 2.5 as you can see in the simulation.How do you explain this?I should obtain 5V insted of 2.5V.Thank You by programerbg December 31, 2014 This the link acctualy: https://www.circuitlab.com/circuit/qvhcmt/differential-amplifier/ by programerbg December 31, 2014 I found the solution.Thank You by programerbg December 31, 2014 Regarding time steps, Garret's suggestion is based on the notes about choosing time steps given here: https://www.circuitlab.com/docs/the-basics/#time_domain_simulation but also note: https://www.circuitlab.com/circuit/d4qjc5/relaxation-osc-fixed-01/ by signality December 31, 2014 How to make square wave with 70ms amplitude and to have posibility to change its duty cycle? by programerbg December 31, 2014 '70mV by programerbg December 31, 2014 The simplest way is to use the PWSREPEAT() source and set up the signal source as a repeated set of time points. A 1kHz 25% duty cycle would be: `PWSREPEAT(0,70m, 250u,0, 1m,0)` See: PWSREPEAT(t1,x1,t2,x2,...) in: https://www.circuitlab.com/docs/expressions/ You could also do it using a Voltage Function generator set to generate a 0V to 1V Triangle or Sawtooth and then use a behavioural source as a comparator with a 70mV output swing by putting this expression into a Voltage Source: `swing/2*(TANH((ref-V(input))*1k)+1)` where: swing = the output voltage swing (from 0 to the value of swing) ref = the value of the duty cycle from 0 to 1. V(input) is the output voltage of the saw or triangle source (which is set to have an offset of 0.5V and an amplitude of 0.5V). So to generate a 25% duty cyle 0 to 70mV signal put this expression into the behavioural source following the saw/triangle source: `35m*(TANH((250m-V(input))*1k)+1)` by signality January 01, 2015