PCB Layouts

Initially I wamted to use one common design/layout for the SensorBox and DisplayBox.  The PCB was designed using ExpressPCB which is free.  The PCB would have the headers to connect the 4x20 character LCD display as well as host the MCP6284 quad Op-Amps for the analog receiving part of the circuit.  The analog part was copied from the mikroElektronika Accessory Board named DistanceMeter.  Its schematic is found below.  Unfortunately I can't find it anymore on their website.  Their Accessory Board was using a Maxbotix MB1100 transducer.

I also went to the Maxbotix web site where I found that their products MB1000 and MB1040 were using the same analog design for processing the received signal with 3 Op Amps in the IC LM324 as shown below.  Pay attention to the similarity in the 2nd half of the circuit, below the PIC16F676.  Maxbotix gives a lot of information in the circuit operation follow the link.

The first PCB which I then designed is shown below.  If you want the native ExpressPCB format email me.

After this design I made a second PCB design shown below, just for the SensorBox.  I had to remove the display from this one as I was going to use the RB0 ~ RB3 ports (pins 21 ~ 24 of the PIC16F886)  for variable gain.  I got the idea for this variable gain receiver or Adaptive Amplifier with increasing Amplification during Echo waiting Time from the following website.  The schematic of the analog part is shown after.  In this design the three Op Amps are in Non-Inverting Amplifier setup.  Its the third Op-Amp which has a variable gain over the time domain for sampling.

The 2nd PCB Analog Schematic is shown below.  Basically its three Op-Amps in Non-Inverting setup in a row with an envelope detector in the end.

The 3rd PCB layout is shown below, hope it solves my problems.  I have added 2 bypass capacitors C4, one near each IC on the circuit whose value would be 0.1 µF/100nF plus 2 other bulk capacitors C21 & C22. C21 vlaue would be 4.7 µF while C22 would be around 1 ~ 2  µF.