Runing out of pins?

[bigz1]

I am currently connecting up my homing/limit switches but running out of pins.

Would this setup be OK?

Pin 10 Limits and E-stop
Pin 11 X homing/limit
Pin 12 A homing/limit(slaved with X)
Pin 13 Y homing/limit
Pin 14 Solid State Relay for router

At present I cant afford a breakout board.

[Oldmanandhistoy]

Hi Bigz1,

Taken from the Turbocnc manual (hope this is ok).

On the parallel port, pins 2-9 are always available for output, which allows at least 4 axes of motion to be controlled. Pins 1,14,16, and 17 can be output also, to control spindles, coolant pumps, and tool changers.
The parallel port inputs are on pins 10,11,12,13, and 15. These are TTL level signals as well. Typical uses for these are spindle encoders, limit switches, and extra logic for detecting when you’ve run out of stock.

Pins 18-25 are ground. Use some of these to shield your cables.

Hope it helps,

John

[bigz1]

On pins 1,14,16 and 17 I am thinking of attaching a terminal block. If I put a pair off 10 K resistors in the terminal at 1 & 14 and 16 & 17, will this be OK? Or do I solder them across the terminal pins under the board?

[Oldmanandhistoy]

On pins 1,14,16 and 17 I am thinking of attaching a terminal block. If I put a pair off 10 K resistors in the terminal at 1 & 14 and 16 & 17, will this be OK? Or do I solder them across the terminal pins under the board?

Would be interested to know why you are using the resistors but I use terminal blocks and 10k resistors for my home and limit switches.

John

[bigz1]

I intend to use 3 off th pins. One for Relay for router the 2ndr for Z Zero plate and the 3rd for a posible tool wear compenstor???(similar to Zero plate but to compensate waer on end mills).

[pminmo]

I would use values lower than 10K for the pullups, specifically 1K. If you wind up with false limits or stops then put a 10K across the switches.

[bigz1]

Got the Relay to work for spindle from pulled up pins today. Thanks guys.

Now I want to add a Zero Plate guess I will have to save up for a breakout board if I want inputs?

[Oldmanandhistoy]

Now I want to add a Zero Plate guess I will have to save up for a breakout board if I want inputs?

If you need more than five input pins you will need another PCI parallel port card as well as a simple connect BOB.

I would use values lower than 10K for the pullups, specifically 1K. If you wind up with false limits or stops then put a 10K across the switches.

I got the info for the 10K resistors from some where not sure now but it could have been from Xylotex.

In simple terms why would you recommend 1K resistors over 10K and will the 10K course problems? I’ve used them now for about two years without any problems that I know of.

John

[kreutz]

If you need more than five input pins you will need another PCI parallel port card as well as a simple connect BOB.



I got the info for the 10K resistors from some where not sure now but it could have been from Xylotex.

In simple terms why would you recommend 1K resistors over 10K and will the 10K course problems? I’ve used them now for about two years without any problems that I know of.

John

Little known detail: micro-switches have a maximum specification for current and a minimum current specification too.

The switches are specified for number of cycles during their lifetime at a specified test switching current. The contact wear consists of mechanical wear and electrical wear.

Mechanical wear makes the gap bigger depending the amount of switching cycles, contact material, and contact force during the lifetime of the switch,
The electrical wear consists of two main mechanisms: arching vaporizing/corroding the contact alloy, and non-conductive contact oxide formation due to environmental conditions. Normal contact arching (within the specified current range) acts as a cleaning mechanism for the oxide layer that develops on the contacts, when that mechanism does not exist due to less than the minimum contact current, the life expectancy decays fast due to false contacts and switching noise.

By using a 1K resistor to VCC you are satisfying the 5 mA minimum current requirement for most of the small signal micro-switches (5- 30 mA @ 30 VDC).

Attaching a small value ceramic capacitor across the switch contacts will help cleaning the contacts by discharging the capacitor when the switch contacts close, and filtering some contact noise due to bouncing.

[Oldmanandhistoy]

Little known detail: micro-switches have a maximum specification for current and a minimum current specification too.

The switches are specified for number of cycles during their lifetime at a specified test switching current. The contact wear consists of mechanical wear and electrical wear.

Mechanical wear makes the gap bigger depending the amount of switching cycles, contact material, and contact force during the lifetime of the switch,
The electrical wear consists of two main mechanisms: arching vaporizing/corroding the contact alloy, and non-conductive contact oxide formation due to environmental conditions. Normal contact arching (within the specified current range) acts as a cleaning mechanism for the oxide layer that develops on the contacts, when that mechanism does not exist due to less than the minimum contact current, the life expectancy decays fast due to false contacts and switching noise.

By using a 1K resistor to VCC you are satisfying the 5 mA minimum current requirement for most of the small signal micro-switches (5- 30 mA @ 30 VDC).

Hi kreutz,

Thank you for the information and your time it is very much appreciated. It’s nice to have a full understanding which you have provided.

I will change the 10K resisters for 1K as soon as I get the time.

Attaching a small value ceramic capacitor across the switch contacts will help cleaning the contacts by discharging the capacitor when the switch contacts close, and filtering some contact noise due to bouncing.

On the subject of switches I have noticed a strong spark through a small hole in the switch when I switch the power on to my drives. This does concern me even though the switch is suitably rated. Do you think this will be damaging the switch to the point it could weld the contacts and would a capacitor help here? It’s switching 45Vdc at around 11Amps; the switch is rated 240V and 13Amps.

John

[bigz1]

Thanks Kreutz for the info. What size would you suggest on the capacitor?

I tried the limit switches today they work but interfere with the stepper motors. Losing steps making unusal noises. Any advice on correcting this would be appreciated? Debounce setting in MACH is at 8000. Steppers work fine as soon as Homing/Limits are disconected. All wire is shielded and earthed in a star pattern.

Liam

[kreutz]

On the subject of switches I have noticed a strong spark through a small hole in the switch when I switch the power on to my drives. This does concern me even though the switch is suitably rated. Do you think this will be damaging the switch to the point it could weld the contacts and would a capacitor help here? It’s switching 45Vdc at around 11Amps; the switch is rated 240V and 13Amps.

John

Are you talking about the main power supply switch or the limit micro-switches?

Every switch has two different ratings: AC and DC. Check that you are reading DC specs. Can you, please post a diagram of your circuit?

1Kohm to VCC and 0.047 to 0.1 uF/ 50V ceramic capacitor across the limit micro-switches will be ok. Take into account that mechanical vibration will trigger your micro-switches depending on their construction. There are specifically designed micro-switches for limit switch applications. Opto-coupler isolation will help rejecting induced noise.