Looks OK to me.

I would link pins 5&6 on the MCP to 0V if you have no use for them.

You could use the spare half of of the MCP for future development.

cheers for the help, ordered the parts on Farnell. I will put it together soon as I get the parts. hope everything goes well.

 

When pin 5 is an open circuit, all 10 LEDs stay lit up. any thoughts why?

 

When pin 5 is an open circuit, all 10 LEDs stay lit up. any thoughts why?

The OPA part of the LM3914 has a high input impedance, so a floating input will pick up external electrical noise.

Why would you want to run it with pin5 o/c .?

 

The OPA part of the LM3914 has a high input impedance, so a floating input will pick up external electrical noise.

Why would you want to run it with pin5 o/c .?

just noticed it when I'm unplugging and plugging the pizzo element. just curious

 

just noticed it when I'm unplugging and plugging the pizzo element. just curious

The input on pin 5 is well protected upto +/-35V.

As the piezo and pin5 are high impedance, you should consider shielding if noise becomes a problem

EDIT:
Is the circuit working as expected.?

 

The input on pin 5 is well protected upto +/-35V.

As the piezo and pin5 are high impedance, you should consider shielding if noise becomes a problem

EDIT:
Is the circuit working as expected.?

LEDs 1,2,3 and sometimes 4 stay lit up no matter what. tryed connecting a 0.27uf capacitor across pin 5 and ground. still didn't sort it out. any ideas?

 

LEDs 1,2,3 and sometimes 4 stay lit up no matter what. tryed connecting a 0.27uf capacitor across pin 5 and ground. still didn't sort it out. any ideas?

With the piezo connected to the input, but with no vibration to the piezo, measure the DC voltage on pin #5 of the LM3914 , post back what you measure.

EDIT:
Also measure pin 3 of the MCP.

 

With the piezo connected to the input, but with no vibration to the piezo, measure the DC voltage on pin #5 of the LM3914 , post back what you measure.

EDIT:
Also measure pin 3 of the MCP.

before seeing this comment, i attached a 100uF parellel to the supply, signal via a 5uF. also i grounded pin 5 via a 30K resistor which seem to have sorted out the issue. i am doing another run of the circuit to check repeatability, ill do the measurements with that circuit.

in the mean time, can you think of any adverse side effect those changes can have?

 

before seeing this comment, i attached a 100uF parellel to the supply, signal via a 5uF. also i grounded pin 5 via a 30K resistor which seem to have sorted out the issue. i am doing another run of the circuit to check repeatability, ill do the measurements with that circuit.

in the mean time, can you think of any adverse side effect those changes can have?

The 100uF and 30K are OK.

Is the 5uF in series with pin 1 of the MCP and pin5 of the LM3914?

 

The 100uF and 30K are OK.

Is the 5uF in series with pin 1 of the MCP and pin5 of the LM3914?

yes it is

 

the circuit is working as expected but at idle there is a current flow of 7.1mA. is there a way to reduce or eliminate this completely without having to use a physical switch. transistor to turn the circuit on and off based on the pizzo elements voltage perhaps?

the circuit as it currently stands

 

Is is it possible for you measure which part of the circuit is sinking 7mA.?

eg: LED' s, LM3914 or OPA

I would expect 2 to 4mA as per the datasheet.

 

Is is it possible for you measure which part of the circuit is sinking 7mA.?

eg: LED' s, LM3914 or OPA

I would expect 2 to 4mA as per the datasheet.

I checked this by having the multimeter in series with the power supply. I'm not sure how to check the mA sink for each section.
how can I check it?

in any case, is there a way to reduce it even further, some sort of electronically operated switch?

 

Came across the term peizo switch, is that something i can incorporate to reduce the quiescent current of 7mA?
can anyone point me in the correct direction?

 

Should that piezo generate a negative voltage, you risk destroying the opamp.

Consider using a Schottky diode to clamp any negative voltage to ground, and insert a 10k resistor between the piezo element and the opamp's noninverting input.

 

Should that piezo generate a negative voltage, you risk destroying the opamp.

Consider using a Schottky diode to clamp any negative voltage to ground, and insert a 10k resistor between the piezo element and the opamp's noninverting input.

That is something I didn't think of, thanks for the advice



Above is the modified circuit

 

t’s working as intended. Based on the amplitude of the signal from the piezo element, it drives the bar graph.
Unfortunately the circuit has a quiescent current of 7mA. Is there a way to reduce this?

I came across a piezo switch based on a 555 that would do the something similar to what I want but unfortunately that circuit itself has a quiescent current of 8mA

Any ideas?

 

Why is a very low standby current, a requirement for this application.?

 

Why is a very low standby current, a requirement for this application.?

it's gonna run off 2 AAs in series and gonna be set in a hard to reach location. having to put fresh ones every 28 days gonna be a pain

 

it's gonna run off 2 AAs in series and gonna be set in a hard to reach location. having to put fresh ones every 28 days gonna be a pain

Is it possible to tell us what the purpose of this project is, just out of technical curiosity.?