Can Shahe TouchDRO board handle 5v tach signal?

[Heyheyjc]

Folks,
I recently got the Shahe-compatible board, and I'd like to hook up my existing tach sensor. It's a Hall effect switch which puts out roughly its supply voltage. An oscilloscope shows it stops working below around 4.7v, so I'd like to power it with the 5v supply.

However...

On the TouchDRO site the Absolute Maximum Ratings table states the tach input can only handle 3.3v, but in a different table says that it's 5v tolerant.

It's likely the latest version of the board, as I've only had it a couple of weeks. Any ideas which is right?

Thanks!
Jake

 

[ycroosh]

Folks,
I recently got the Shahe-compatible board, and I'd like to hook up my existing tach sensor. It's a Hall effect switch which puts out roughly its supply voltage. An oscilloscope shows it stops working below around 4.7v, so I'd like to power it with the 5v supply.

However...

On the TouchDRO site the Absolute Maximum Ratings table states the tach input can only handle 3.3v, but in a different table says that it's 5v tolerant.

It's likely the latest version of the board, as I've only had it a couple of weeks. Any ideas which is right?

Thanks!
Jake

Jake,
The 5V tolerant part is an error I made in the description (mi-copy/paste). Tachometer and probe inputs are pulled up to 3.3V, so 5V on those pins will create problems. The maximum ratings table is correct.
Thank you
Yuriy

 

[Heyheyjc]

Thanks for responding Yuriy. Any recommendations for a suitable sensor? Most I've seen are 6v and up.

Jake

 

[Heyheyjc]

Jake,
The 5V tolerant part is an error I made in the description (mi-copy/paste). Tachometer and probe inputs are pulled up to 3.3V, so 5V on those pins will create problems. The maximum ratings table is correct.
Thank you
Yuriy

Thanks for responding Yuriy. Any recommendations for a suitable sensor? Most I've seen are 6v and up.

Jake

 

[ycroosh]

Thanks for responding Yuriy. Any recommendations for a suitable sensor? Most I've seen are 6v and up.

Jake

Jake, you can just use a voltage divider to drop the voltage. You have 5V pin next to the USP power port. Use that to power the sensor and then use 2/3 ratio resistor voltage divider (i'd start with 20K/30K and see how it behaves).

 

[Heyheyjc]

Jake, you can just use a voltage divider to drop the voltage. You have 5V pin next to the USP power port. Use that to power the sensor and then use 2/3 ratio resistor voltage divider (i'd start with 20K/30K and see how it behaves).

Great, I'll try that, thanks.

 

[Heyheyjc]

Jake, you can just use a voltage divider to drop the voltage. You have 5V pin next to the USP power port. Use that to power the sensor and then use 2/3 ratio resistor voltage divider (i'd start with 20K/30K and see how it behaves).

Well... Turned out just a voltage divider wasn't enough, but I improvised a sort of NOT gate using a transistor and that did the trick. My electronics skills are rudimentary.

However...

Having got it all tested and working beautifully and feeling super proud of myself, I forgot to unplug my mill while fitting it all in the power box, touched something to 110v, blew a fuse and fried both the TouchDRO board and my scales. Sigh.

Expect another order soon.