Dynomotion

Group: DynoMotion Message: 15160 From: ben@dmsdesignco.com Date: 11/14/2017
Subject: SnapAmp 5V LVTTL as an encoder index

Hi Tom,


I have a question for you concerning GPIOs on the JP7 port of the SnapAmp.


Typically, we would use optos for our encoder indexes, however in our latest build we have utilized all 8 of the optos. We are looking to use a couple of GPIOs on the SnapAmp for the motor index, the encoder index is a 5V signal, and I under the impression that the GPIOs from pin 1 to 14 are 5V tolerant. 


While tuning the motors, the bit's state would occasionally flicker, causing us issues. If the problem is a floating logic state, I believe a pull-down resistor would solve it... However I wanted to ask you if there was a specific resistor value that you would recommend, or if you have an alternative solution?


Thanks. 

With best regards,

Ben Stevenson
Group: DynoMotion Message: 15162 From: Tom Kerekes Date: 11/14/2017
Subject: Re: SnapAmp 5V LVTTL as an encoder index
Hi Ben,

The SnapAmp GPIO's are 5V tolerant.  They are high impedance inputs that may float high or low if not connected and driven.  I'd suggest a pull down resistor that can be driven high with 5ma of current:

R = V / I = 5V / 5ma = 1K

HTH
Regards
TK



On 11/14/2017 7:14 AM, ben@... [DynoMotion] wrote:
 

Hi Tom,


I have a question for you concerning GPIOs on the JP7 port of the SnapAmp.


Typically, we would use optos for our encoder indexes, however in our latest build we have utilized all 8 of the optos. We are looking to use a couple of GPIOs on the SnapAmp for the motor index, the encoder index is a 5V signal, and I under the impression that the GPIOs from pin 1 to 14 are 5V tolerant. 


While tuning the motors, the bit's state would occasionally flicker, causing us issues. If the problem is a floating logic state, I believe a pull-down resistor would solve it... However I wanted to ask you if there was a specific resistor value that you would recommend, or if you have an alternative solution?


Thanks. 

With best regards,

Ben Stevenson
Group: DynoMotion Message: 15164 From: ben@dmsdesignco.com Date: 11/14/2017
Subject: Re: SnapAmp 5V LVTTL as an encoder index
Hi Tom,

Thank you for your prompt solution. Have a great day.
-Ben