# 555 Astable Timer produces incorrect period/frequency

I am building a 555 astable timer circuit for a course which must match the BPM of a song. The song has a BPM of 104, which requires a timer frequency of roughly 1.733 Hz.

The circuit looks as follows:

(the green wires go off to the left onto another breadboard, which looks as follows:)

It is hard to see, but the 0.01µF capacitor goes to pin 5 of the 555 timer.

The values used in the circuit as follows (measured using a LCR meter): R1 = 5.5kΩ R2 = 38.5kΩ Ctotal = 10.02 µF

The problem is that the circuit produces a frequency of roughly 1.5, far off the from the desired/predicted frequency of 1.733. 5V Power is being supplied to both rails, the chip has been replaced, but to no avail. Here is a picture of the simulated circuit in LTspice:

Is this due to some limits of the 555 timer at frequencies nearing 1Hz or due to some miswiring on my part?

simulate this circuit – Schematic created using CircuitLab

• It is hard to see, but the 0.01µF capacitor goes to pin 5 of the 555 timer. - yes, that's why we demand schematic diagrams (use the diode/capacitor/resistor button on the toolbar) rather than photos of assembled circuits. Commented Oct 17, 2018 at 18:09
• The axial electrolytic capacitors appear to say 1 uF 50 V, and they are in series. How do they add up to 10 uF, am I looking at the wrong picture? Also, 10.02 uF is very accurate for an electrolytic capacitor, 0.2%, they're typically ±20%, are you sure the measurement was OK? Commented Oct 17, 2018 at 18:51
• Am still suspicious of those electrolytics. They are "not very good" in many ways. It is possible that your LCR meter measures C in a way that differs from the way it is used by the LM555. Commented Oct 17, 2018 at 19:26
• Expecting such a precise value of f when using components with at least 10% tolerance is not practical. Make your frequency dependent from a potentiometer and calibrate it afterwards. But be warned, even with this trick, your frequency will vary with temperature. Commented Oct 17, 2018 at 20:16
• "The 10µF is not very good and has a capacitance of <9.5µF". What's not good about that? Electrolytic caps are typically specified with a pretty broad tolerance. I suspect you're well within specs on that one. Commented Oct 17, 2018 at 21:37