# Step circuit

Discussion in 'General Electronics Chat' started by karas, Aug 15, 2014.

1. ### karas Thread Starter Active Member

Sep 8, 2011
84
0
Hi I need to build steps circuit the circuit increase one volt each one step and the time for each step is one second,so can someone help me
thanks

2. ### MikeML AAC Fanatic!

Oct 2, 2009
5,450
1,066
How many total steps?

What happens at the last step?

Counter driving a DAC comes to mind...

karas likes this.
3. ### absf Senior Member

Dec 29, 2010
1,462
356
How much current for the output of the voltages stepped and what is the MAX output voltage ? Can you use mcu or just discrete logic chips ?

Allen

karas likes this.
4. ### wmodavis Well-Known Member

Oct 23, 2010
737
149

Use a binary counter fed by a 1 Hz clock signal and feed the counter outputs into an D/A.

karas likes this.
5. ### ScottWang Moderator

Aug 23, 2012
4,783
762
You might talk some more details.

If you using the normal DAC, it could be too many steps for each step 1V, so using a binary counter and 4 bits r2r dac circuit, you also need a 1Hz oscillator as this.

karas likes this.
6. ### crutschow Expert

Mar 14, 2008
12,565
3,079
There's no reason to build a complex discrete DAC circuit. Just use a standard 8-bit DAC and toggle only the higher order bits you need to generate the required steps. For example the upper three bits could give you seven 1V steps by proper scaling of the output.

How high do you want these one volt steps to go (what's the maximum output voltage)?

karas likes this.
7. ### karas Thread Starter Active Member

Sep 8, 2011
84
0
it is vey low current (5 milli amp) and max out put voltage is 10 v

8. ### ScottWang Moderator

Aug 23, 2012
4,783
762
For a not precisely method, using NE555, CD4017 and some 1n4148, some resistors.

NE555(1Hz) → CD4017(counter) → 1N4148 → Voltage divider(resistors) → Vout

1N4148 x10, 10 resistors and one common resistor for voltage divider.

karas and absf like this.
9. ### crutschow Expert

Mar 14, 2008
12,565
3,079
What do you want it to do after it reaches 10V, reset and start again from 0V?

karas likes this.
10. ### crutschow Expert

Mar 14, 2008
12,565
3,079
Below is the simulation of a circuit, as Scott suggested, with a 555 clock, a binary counter, and an R-2R ladder network with an op amp and transistor buffer output that gives ten 1V, 1 second steps and then repeats.

Is that more or less what you want?

Edit: The +12V power and ground connections to the counter and the AND gate are not shown.

Note that for best accuracy/stability you can use two 10kΩ resistors in series to make the 20kΩ resistance values. That also simplifies the part's list, although at the expense of more parts.

Last edited: Aug 16, 2014
karas, ScottWang and absf like this.
11. ### karas Thread Starter Active Member

Sep 8, 2011
84
0
After reach 10 v it stays and reset and start again when I enabled again

12. ### karas Thread Starter Active Member

Sep 8, 2011
84
0
it works perfect , thanks so much

13. ### karas Thread Starter Active Member

Sep 8, 2011
84
0
what is the function of the transistor in the circuit and when Q1 is high what is vbin and vout and also when Q1and Q2 are on what is the value of vbin and vouto

Last edited: Aug 17, 2014
14. ### Brownout Well-Known Member

Jan 10, 2012
2,375
998
The transistor provides some isolation from the load. It helps prevent changes in load current from affecting output voltage.

karas likes this.
15. ### karas Thread Starter Active Member

Sep 8, 2011
84
0
please what is the values of vbin at different steps and also vout and what is the REASON of USING the transistor

Last edited: Aug 18, 2014
16. ### crutschow Expert

Mar 14, 2008
12,565
3,079
The value for Vbin is shown on the graph and is approximately .747 of the desired Vout which is why the op amp has a gain of 1.338. The Vout steps are 1V.

What do you mean by "value of the transistor". It's shown as a 2N2222 but most small NPN transistors will work. Its purpose is to provide more output current than the op amp can supply.

Note that the circuit I posted cycles continuously. If you need it to stop at the end and return to 0V (or stay at 10V) until a switch is actuated to repeat the cycle, then I can modify the circuit for that.

Last edited: Aug 18, 2014
karas likes this.
17. ### karas Thread Starter Active Member

Sep 8, 2011
84
0
sorry i mean the reason of using the transistor

18. ### crutschow Expert

Mar 14, 2008
12,565
3,079
The transistor is a voltage follower to boost the output current since the 5mA you mentioned may be near the limit of what the op amp can deliver. But if the output load is never lower than 2kΩ you can eliminate the transistor and just connect R15 directly to the op amp output.

karas likes this.