In the circuit description it said 4538b, but after googling the diagram of this IC, it seems there is no schmitt trigger on the input as it shows on the photo. Does CD14538BE work for this application. What is the best option? Thanks
Look at the data sheet here. Look at Figure 2 on page 3. Both inputs are Schmitt triggers, but the functionality is not shown on the active-low input since it is tied to Vcc.