# Help for schem mod (quantizer)

**URL:** <https://lookmumnocomputer.discourse.group/t/help-for-schem-mod-quantizer/874>\
**Category:** DIY STUFF\
**Created:** [May 13, 2020, 2:08pm UTC](https://lookmumnocomputer.discourse.group/t/help-for-schem-mod-quantizer/874 "2020-05-13T14:08:32Z")\
**Posts on this page:** 1\
**Showing post:** 33

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**Author:** ![fredrik](https://yyz2.discourse-cdn.com/free1/user_avatar/lookmumnocomputer.discourse.group/fredrik/32/682_2.png) [@fredrik](https://lookmumnocomputer.discourse.group/u/fredrik)\
**Post date:** [May 13, 2020, 7:14pm UTC](https://lookmumnocomputer.discourse.group/t/help-for-schem-mod-quantizer/874/33 "2020-05-13T19:14:12Z")

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Yeah, using shottkys as “clamping diodes” is a common pattern (see e.g. the BAT42s and 1N5817s mentioned earlier). They have a low forward voltage, so the input signal won’t get very far above or below the supply rails before it’s shorted away. Zeners have a somewhat different behaviour, though; they’re used backwards, and open when the reverse voltage exceeds a certain voltage.

(but I guess I just answered my own question – with shottkys, the one connected to ground will start conducting when the input voltage goes below −0.3 V or so, but with zeners the diode in the same position will start conducting when the input voltage goes _above_ the zener voltage.)

(Note btw that the Arduino pins have [internal clamping diodes](https://lookmumnocomputer.discourse.group/t/1222-tuner-vco-module/16/47), so if you can limit the current you can just rely on them. External ones are perhaps more robust, and definitely easier to replace, though 🙂)

EDIT: Below −0.3 V, that is – i.e. one shottky diode drop from 0 V. Similar in the other direction.

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