4
\$\begingroup\$

In a schematic I've been reviewing I see in only one spot that there is a 1/2v going somewhere? What does that mean?

schematic

simulate this circuit – Schematic created using CircuitLab

enter image description here

\$\endgroup\$
  • 2
    \$\begingroup\$ The schematic you've laid out here doesn't make sense, because a ground symbol is what we consider to be 0 V so marking it with a voltage is contradictory. Could you provide a photo/screenshot of the original schematic rather than your redrawing? There might be some subtlety missing. Other context such as what the schematic is supposed to be a part of, or demonstrate, might also be useful. (But thanks for taking the time to do the embedded schematic — it's usually better than alternatives!) \$\endgroup\$ – Kevin Reid May 7 at 3:38
  • \$\begingroup\$ @KevinReid I've added the full schematic and highlighted the spots that the 1/2v shows up (it in two places actually) \$\endgroup\$ – greyBow May 7 at 3:42
  • 2
    \$\begingroup\$ @greyBow It just means, in this case, \$4.5\:\text{V}\$. \$\endgroup\$ – jonk May 7 at 3:46
  • 3
    \$\begingroup\$ @greyBow NO NO NO! Look at the two \$10\:\text{k}\Omega\$ resistors, \$R_{20}\$ and \$R_{21}\$!!! \$\endgroup\$ – jonk May 7 at 4:01
  • 3
    \$\begingroup\$ :( that symbol choice was pretty bad (especially in addition with this ground symbol instead of 3 lines) \$\endgroup\$ – Wesley Lee May 7 at 4:05
12
\$\begingroup\$

Look at the top of R20 - that is labeled V and is the supply rail. (V is also connected to 9VDC which is the power input - see the DC connector and battery, towards the top left of the schematic.)

Therefore, as commented by jonk, the node at the junction of equal resistors R20 and R21 must be half of V hence 1/2V means exactly that.

Also, looking carefully, the arrow symbols labeled 1/2V are slightly smaller than the arrows which are the ground symbol. On the full schematic you can compare their size and see the difference - but otherwise, that choice of arrow by the designer could easily be confusing! As kindly pointed out by Kevin in the comments, that smaller arrow is being used here as the symbol for a named node.

\$\endgroup\$
  • 1
    \$\begingroup\$ Might be worth pointing out that the same arrow symbol is used to connect "9VDC". So it's a general named node symbol. \$\endgroup\$ – Kevin Reid May 7 at 4:02
  • \$\begingroup\$ Thank you for the explanation, so then does that mean that 1/2v coming off the junction between r20 and r21 would then connect to the 1/2v coming off of R2? \$\endgroup\$ – greyBow May 7 at 4:07
  • \$\begingroup\$ @greyBow Yes. Those nets are tied together. \$\endgroup\$ – jonk May 7 at 4:09
  • 1
    \$\begingroup\$ I see. Thank you SO much for the help, this has been extremely helpful. Many, many thanks! \$\endgroup\$ – greyBow May 7 at 4:11
  • 1
    \$\begingroup\$ That wording is confusing as well. I would label it V/2 or something; "1/2V" makes me think it means 0.5V. \$\endgroup\$ – Hearth May 7 at 14:39
6
\$\begingroup\$

The down arrow below R2 in the original schematic is not a Ground symbol - it indicates "this point is connected to something that-a-way" - it connects to an upward-pointing arrow in the power supply section below. That point will be at half the 9 V power supply voltage due to R20 and R21. It provides an appropriate bias voltage for Q1.

Drawing a line to show the connection would make much more sense.

Edit: as @kevin pointed out, that narrow arrow symbol is used as a general named signal marker - all such arrows with the same name will be connected together.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.