# Control emitter with external Siemens PLC / Number of parts

**URL:** <https://community.factoryio.com/t/control-emitter-with-external-siemens-plc-number-of-parts/1851>\
**Category:** Drivers\
**Created:** [January 4, 2023, 8:21am UTC](https://community.factoryio.com/t/control-emitter-with-external-siemens-plc-number-of-parts/1851 "2023-01-04T08:21:57Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![stescarpelli](https://avatars.discourse-cdn.com/v4/letter/s/76d3ee/32.png) [@stescarpelli](https://community.factoryio.com/u/stescarpelli)\
**Post date:** [January 4, 2023, 8:21am UTC](https://community.factoryio.com/t/control-emitter-with-external-siemens-plc-number-of-parts/1851/1 "2023-01-04T08:21:57Z")

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Hello together

Is there a way to give the emitter exactly the number of parts it should output?

I have a Siemens S7 1215C and a HMI and want to control the FactoryIO via it. The color selection already works. The number of parts are counted by a CounterUp how many times the emitter is set to 1.  
Actual state: always one part less than specified.

 ![image](https://europe1.discourse-cdn.com/flex017/uploads/factoryio/original/1X/5dd40f660ca8fdd45a75a9c6eab687844e7ddab3.png)

Thanks for your help and inputs.

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**Author:** ![bartosz.kuras00](https://avatars.discourse-cdn.com/v4/letter/b/a9a28c/32.png) [@bartosz.kuras00](https://community.factoryio.com/u/bartosz.kuras00)\
**Post date:** [January 4, 2023, 7:03pm UTC](https://community.factoryio.com/t/control-emitter-with-external-siemens-plc-number-of-parts/1851/2 "2023-01-04T19:03:27Z")

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For me the easier solution is to use retroreflective sensor, if you set max time and min time to 1 you should be able to count one part before next is emited and stop the enable (emit) signal.

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**Author:** ![drazen.pondeljak](https://avatars.discourse-cdn.com/v4/letter/d/35a633/32.png) [@drazen.pondeljak](https://community.factoryio.com/u/drazen.pondeljak)\
**Post date:** [January 6, 2023, 2:26pm UTC](https://community.factoryio.com/t/control-emitter-with-external-siemens-plc-number-of-parts/1851/3 "2023-01-06T14:26:11Z")

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Agree with bartosz.kuras00. Have a look at _Scene 4 - Queue of items (Counters)_.